Composite Supraparticles with Tunable Light Emission
- Federico Montanarella ,
- Thomas Altantzis ,
- Daniele Zanaga ,
- Freddy T. Rabouw ,
- Sara Bals
, - Patrick Baesjou ,
- Daniel Vanmaekelbergh, and
- Alfons van Blaaderen
View Author Information
‡ †Condensed Matter and Interfaces and ‡Soft Condensed Matter, Debye Institute for Nanomaterials Science, Utrecht University, P.O. Box 80000, 3508 TA Utrecht, The Netherlands
§ EMAT, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium
*E-mail: [email protected]
Copyright © 2017 American Chemical Society
ACS AuthorChoicewith CC-BY-NC-NDlicense
Abstract
Robust luminophores emitting light with broadly tunable colors are desirable in many applications such as light-emitting diode (LED)-based lighting, displays, integrated optoelectronics and biology. Nanocrystalline quantum dots with multicolor emission, from core- and shell-localized excitons, as well as solid layers of mixed quantum dots that emit different colors have been proposed. Here, we report on colloidal supraparticles that are composed of three types of Cd(Se,ZnS) core/(Cd,Zn)S shell nanocrystals with emission in the red, green, and blue. The emission of the supraparticles can be varied from pure to composite colors over the entire visible region and fine-tuned into variable shades of white light by mixing the nanocrystals in controlled proportions. Our approach results in supraparticles with sizes spanning the colloidal domain and beyond that combine versatility and processability with a broad, stable, and tunable emission, promising applications in lighting devices and biological research.
Even after more than two decades of extensive research, the optical properties of colloidal semiconductor nanocrystals, also known as quantum dots (QDs), (1) continue to intrigue researchers in nanophotonics, materials science and biology. Compared to solid-state QDs, colloidal QDs have a smaller and more easily tunable size. (2) This means that, due to strong exciton confinement, the light emission is tunable over a wide wavelength range in the visible or near-IR. Moreover, epitaxial engineering in core–shell systems has advanced remarkably over the past decade. This resulted in photochemically stable QDs with photoluminescence (PL) quantum yield close to unity. (3, 4) Furthermore, the control over epitaxial core–shell synthesis enabled the community to explore new degrees of freedom brought by engineering of the exciton wave functions, (5) resulting in reduced Auger recombination, (6-8) brighter multiexciton emission, and lower lasing thresholds. (9-11) There is no doubt that following these recent advances, colloidal QDs will be used in a wide variety of applications, ranging from biological research (12-14) to luminescent light concentrators (15-17) and displays. (18)
Nowadays, two of the most important applications of colloidal QDs are their use as spectral conversion phosphors in light-emitting diodes (LEDs) and in (the backlight of) liquid crystal (LC) displays. In LEDs aimed at general lighting applications, the main role of QDs is to partially convert the primary blue light from the LEDs into multicolored light, with a spectrum matching human needs. In LED technology, where a high power efficiency is paramount, QDs have shown to be valuable for two different reasons: (i) they have a high quantum yield, and (ii) they are narrow band emitters. When QDs are used as a red phosphor instead of traditional wide-band red emitters, the red emission of an LED lamp is possible without losing photons in the near-IR, thereby significantly boosting the power efficacy (lumen/watt) of the lamp. Additionally, by using mixtures of differently colored QDs, it is relatively easy to achieve a high color rendering index lamp (CRI > 90), compared to traditional phosphors. Regarding display technology, QDs have shown to be valuable for their size-dependent tunable, narrow-band emission, which enables a strong matching of the backlight emission with the color filters of the display, thereby enhancing brightness and color saturation. In displays, QDs are already applied commercially. In order to strengthen these properties and enhance the suitability of QDs for industrial applications, especially for white light emission, several approaches have been proposed: QDs doped with metal ions, (19, 20) ultrasmall CdSe QDs, (21, 22) or QDs that show a relatively broad spectrum due to multiexciton emission (23) or shell emission. (24) All of these materials show only partially tunable emission spectra. Moreover, the spectra change with the intensity of the excitation, thus hampering several applications. A simple approach would be to mix three types of colloidal semiconductor QDs with emission in the red, green, and blue, respectively. In this respect, attempts based on mixed thin films of QDs have been reported. (25)
Here, we report an approach that results in spherical supraparticles (SPs) that are composed of QDs emitting in the red, green, and blue. By controlling the ratios of QDs per SP, we can easily and rationally tune the spectrum of the SPs, and the emission spectrum is independent of the excitation intensity in a wide range. The SPs are charge- and sterically stabilized colloids themselves and can be dispersed in many industrially relevant polar solvents, including water. In addition, their much larger size as compared to individual QDs also makes them easier to process in an industrial setting. Our work presents a platform for easily processable colloidal particles with a bright and stable (non-blinking) emission of pure or composite color, tunable in the entire visible range. Such a platform holds promise for displays as well as optoelectronical and biological applications.
Results/Discussion
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Synthesis and Composition of the Tunable Emitting SPs
The first step in the realization of SPs is to synthesize the constituent QDs. For this, we adapted existing protocols for stable red, green, and blue emitting Cd(Se,ZnS) core/(Cd,Zn)S shell QDs (Figure 1) (see SI for further information).
Figure 1
Figure 1. TEM images and optical properties of the original QDs. (a–c) Representative transmission electron micrographs (scale bar 50 nm) of (a) the red emitting QDs (diameter: 10.3 ± 1.0 nm), (b) the green emitting QDs (diameter: 11.0 ± 1.1 nm), and (c) the blue emitting QDs (diameter: 10.5 ± 1.3 nm). Insets are models of the QDs. (d–f) Absorption (dashed lines) and emission (solid lines) spectra of three different populations of QDs used for the self-assembly.
Our general approach for the self-assembly of the SPs is based on the drying of an oil-in-water emulsion at elevated temperatures (68 °C) as described previously (26, 27) (details given in the SI). In Figure S1 the synthesis procedure is schematically presented. The emulsification is performed through a methodology developed by the Bibette group that uses high shear rates generated in a Couette shear cell (28) combined with the viscoelasticity of a concentrated emulsion; this leads to fairly monodisperse breakup of the droplets. In this manner, SPs with a precise size can be produced in a size range between 100 nm and several micrometers (Figure.S2).
The three types of QDs that are incorporated in the SP are of similar size, and they have the same inorganic outer shell (ZnS) and organic ligands (oleic acid). However, the sizes are different enough that the effective polydispersity of the mixture is above 10%, which should prevent crystallization of the QDs into a long-range ordered superstructure. We therefore expect that the three types of QDs will be randomly packed and homogeneously distributed in the SPs in proportion to their concentration in the precursor suspension of mixed QDs.
Structural Characterization of the SPs
The surface structure of the as-prepared SPs can be studied by detection of secondary electrons (SE) in a scanning transmission electron microscope (STEM) (Figures 2a and S3). To investigate the inner structure of the SPs, high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) is combined with electron tomography (29, 30) (Figure 2b–e). Hereby, a tilt series of HAADF-STEM images (Figure 2b) is acquired along different viewing directions and is combined into a three-dimensional (3D) reconstruction (Figure 2c) using a mathematical algorithm (see SI). In Figure 2d we present a slice through the 3D reconstruction yielding the internal structure. This image as well as the fast Fourier transform in Figure 2e clearly show that the QDs are not ordered in the SPs, thus forming an amorphous glassy structure, as expected. In order to investigate the type of packing in the assemblies in more detail, the coordinates extracted from the tomography reconstruction were used to calculate bond order parameters. (31, 32) The analysis excluded the presence of periodic arrangements of particles. It was shown previously (26) that if the composing QDs have the same size and a regular spherical shape and their interactions can be approximated well with that of a hard-sphere potential, then the SPs form crystalline structures with an icosahedral or face-centered cubic structure. In our case, the composing QDs mixtures are characterized by a relatively high polydispersity and an irregular shape; this leads to a random arrangement of the QDs inside the SPs with a high packing fraction. This is confirmed by the radial distribution function (RDF) (Figure S4), which is calculated through the identification of the single QDs inside a SP (Figure S5). The RDF shows an average distance between nearest neighbors of 10.9 nm, which is in agreement with the particle size derived from TEM images.
Figure 2
Figure 2. Structural characterization of the SPs. (a) SE-STEM image of two SPs (scale bar 200 nm). The inset shows a magnification of one of the particles (scale bar 20 nm). Individual QDs can be clearly distinguished. (b, c) 2D HAADF-STEM images (scale bars 50 nm) of a small SP for which electron tomography has been performed (b), and a 3D visualization of the 3D tomographic reconstruction of the same SP (c). (d) Slice through the center of the 3D reconstruction of the SP (scale bar 50 nm). Individual QDs can be clearly recognized as well as their relative position, showing the irregular inner structure. (e) Fast Fourier transform of the slice of panel d (scale bar 0.1 nm–1).
The 3D analysis of the SPs by electron tomography also enables us to verify whether the QDs are homogeneously mixed in each of the SPs. In Figure S6a–c, HAADF-STEM images acquired from the individual red, green, and blue population are presented. The shape of the red emitting QDs is more spherical in comparison to the other types. The intensity in HAADF-STEM images depends on the atomic number Z. Energy dispersive X-ray spectroscopy (EDS) measurements on the individual QDs (Figures S7–S10) show that the red emitting particles contain a higher amount of Cd in their structure compared to the green and blue ones (Table S1). In this manner, we conclude that the high intensity particles in the orthoslices correspond to red emitting particles. Visual inspection of the QDs in the orthoslices in Figure 2d shows that the different QDs are homogeneously mixed in each SP. The homogeneous distribution of the QDs in the SPs was further confirmed by EDS measurements (Figure S11). From Figure S11 it is clear that all the elements, and in particular Se (which is not present in the blue emitting QDs), were found to be homogeneously distributed inside the SP, thus supporting our statements about the homogeneous distribution of the QDs inside the SPs.
Optical Characterization of Individual SPs and Ensembles
We use confocal microspectroscopy to study the optical properties of our SPs (Figure 3). Microscopy of individual micron-sized SPs, larger than the diffraction limit, demonstrates that the emission of the red, blue, and green light does not vary spatially within a SP (Figures 3a,b and S12). This agrees with the homogeneous mixing of the QDs in each SP as derived from electron tomography measurements (see above). Confocal microscopy also confirms uniform emission spectra among all SPs in one batch. Even SPs from one synthesis batch but with different sizes show similar PL emission spectra (Figures 3c–e and S13).
Figure 3
Figure 3. Optical characterization of the SPs. (a) Confocal microscopy image of a set of SPs drop-casted and dried on a glass slide and excited with UV excitation (scale bar 3 μm). (b) Confocal fluorescence image of different SPs (scale bar 1 μm). The blue-green emission (450–550 nm) is shown in green, while the red emission (600–700 nm) is shown in red; the image is deconvolved through the modeling of the point spread function of the microscope. The inset shows the signal collected along the white line drawn in the figure coming from the two detectors. (c–e) Emission spectra of some of the SPs presented in panel a, indicated with the green, red, or blue frame.
Using (time-resolved) PL spectroscopy, we study in more detail how the ensemble-averaged optical properties of the SPs relate to those of the separate constituent QDs (Figure 4). In Figure 4a the emission spectra are compared. The contributions from the separate NC populations (colored lines) are clearly distinguished in the composite emission spectrum of the SP (black). This is to be expected because (i) the constituent QDs are too far apart to exhibit quantum mechanical coupling that could otherwise change the energy levels and (ii) the SPs are too polydisperse for whispering gallery modes (27) to appear in the ensemble emission spectrum. Nevertheless, the peak position of the blue contribution to the SP emission (black line) is slightly red-shifted from the peak position of the dispersion of blue QDs (blue). This indicates energy transfer among blue QDs in the SP and/or from blue QDs to the green and red QDs. Most likely, both Förster-type energy transfer (i.e., by dipole–dipole coupling) and photon reabsorption contribute to this. We wish to remark that the emission spectrum of the composed SPs is independent of the excitation intensity in the broad range of single exciton excitation (up to 14 mW) (Figure S14). This is an important asset compared to previous proposals in which a broad emission was reached by simultaneous exciton and biexciton emission (23) or shell emission. (24)
Figure 4
Figure 4. Optical properties of SPs compared to suspensions of the constituent QDs. (a) Emission spectrum of an ensemble of white light-emitting SPs (black) and of the three separate dispersions of the constituent QDs (colored; each scaled to match the maximum intensity of the corresponding peak in the composite spectrum). (b) PL decay traces of red QDs freely dispersed in toluene (red closed circles), assembled in water-dispersed SPs of red QDs (red open circles), and assembled in a white light-emitting SPs (gray open circles). The red line is a fit to the PL decay of red SPs, and the black line to the decay of white-light emitting SPs (see Supporting Information for an explanation of the fitting procedure). Same for (c) green QDs and (d) blue QDs.
In Figure 4b–d we show the PL decay dynamics of the three batches of QDs freely dispersed in toluene (closed circles) compared to QDs assembled into a SP (open circles). The suspension of the red emitting QDs shows the slowest PL decay, followed by the green and the blue emitting QDs, qualitatively in agreement with the frequency dependence of the optical transition strengths. (33) The decay dynamics of the same batches of QDs assembled in water-dispersed SPs are consistently faster. More precisely, the PL of SPs consisting purely of red QDs (red open circles) decays 66% faster than that of freely dispersed QDs in toluene (see Supporting Information for a description of our analysis procedure). The decay of the red component in mixed white light-emitting SPs (black open circles) is 33% faster than the red NC dispersion. For the green emission, these acceleration factors are 41% for the purely green SPs and 32% for the mixed SPs; for the blue emission 29% and 211%.
Multiple collective effects simultaneously affect the decay dynamics in the SPs. For example, the local density of optical states (LDOS), which determines the rate of radiative decay, is higher for QDs in a SP than for those freely dispersed in toluene. We estimate the LDOS in a SP using a simplified model, where the SP is assumed to be a perfect sphere with a homogeneous refractive index, which can support Mie resonances (Figure S15). This model predicts that the LDOS, averaged over the volume of the SP and orientation of the transition dipole moments, is approximately two times larger in a SP than for free QDs (Figure S15). Indeed, the PL decay in SPs is always faster than for dispersed QDs (Figure 4b–d). However, the acceleration is less pronounced than the simplified Mie model predicts, which can in part be due to damping of the Mie resonances by refractive index inhomogeneities and absorption in the SP. Moreover, the PL decay dynamics observed can be affected by Förster energy transfer among QDs and reabsorption of emitted light.
We can get some insight into the occurrence of Förster energy transfer in the SPs by comparing the PL decay dynamics in pure-color SPs (colored open circles in Figure 4b–d) and mixed white light SPs (gray open circles). In pure-color SPs energy transfer can occur only among QDs from the same (inhomogeneously broadened) color population. Mixed SPs enable additional transfer between populations from blue to green, blue to red, and green to red. Indeed, the blue PL decay (Figure 4d) is faster in mixed SPs than in pure SPs because of these additional decay channels. The red PL (Figure 4b) is slower in mixed SPs, because the red QDs are fed through energy transfer from the blue and green populations. The green PL decay is approximately equally fast in pure and mixed SPs, which indicates that the effects of feeding from the blue population and transfer to the red compensate each other. Detailed modeling of these energy-transfer processes and their effect on the color output depends on many factors (e.g., the degree of inhomogeneous broadening and the separations and relative orientations of the QDs in the SP). This is beyond the scope of the current work. Nevertheless, these effects must be taken into account in the composition of the SPs if a certain desired shade of white light is targeted (see below), and in our case this was done empirically.
Lighting applications require photochemically stable SPs, while many biolabeling applications require time-constant emission from individual SPs, without blinking or dark periods. Our SPs show bright, non-blinking, and non-bleaching emission on the single-SP level over a time period of at least 3000 s (Figure S16). This stability is an important asset compared to conventional optical labels, for example, silica particles filled with organic dyes such as rhodamine isothiocyanate (RITC). (34) Concerning the non-blinking feature, we remark that this is due to the concomitant emission of many QDs in each SP. We also remark that the size of the SPs can be tuned up to 100 nm, that they can be dispersed in water, if needed, coated by a thin silica layer, and that the surface can be biofunctionalized at will. Thus, the NC SPs presented here, emitting one color or a combination of two or three fundamental colors, are suitable as biological labels.
For application of the SPs as spectral conversion phosphors in lighting, the precise tunability of the white light spectrum is of great importance. To study this, we convert the pure spectra of the constituent QDs and the composite spectra of the SPs to coordinates of the Commission Internationale de l’Éclairage (CIE) chromaticity space (Figure 5). The vertices of the triangle are the coordinates of the three QDs components. The better the color purity of the single NC components, the larger the area of the triangle in the CIE space. The area inside the triangle represents all the colors that can be achieved by composing SPs from the three different QDs used here. The color purity of the QDs, as used here, is another important advantage of NC SPs over regular phosphors that usually have a broad emission spectrum. The black dots within the triangle in Figure 5 represent color points that we obtained by assembling our QDs into SPs. A given broad SP emission spectrum can be achieved and fine-tuned if one knows the emissive strength of the red, green, and blue emitting QDs and takes the lower effective emission yield from the blue-emitting particles into account, in a few experimental iterations (see Figure S17). We remark that a targeted composite emission spectrum will remain independent of excitation intensity over a broad excitation regime as long as the steady-state exciton population remains below unity.
Figure 5
Figure 5. CIE chromaticity diagram of the QDs and the SPs. Left: CIE diagram representing different SP batches as obtained by changing the ratio between the three QDs populations. The vertices of the triangle represent the coordinates of the three types of QDs. Therefore, the area of the triangle represents all the possible colors SPs can have. Right (1–3): Digital true-color photographs of the QDs dispersed in solution when illuminated with a UV laser. (4) Digital photograph of a dispersion of the SPs, composed of the three types of QDs, emitting white light.
Conclusions
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We have reported the synthesis and structural and optical characterization of colloidal water-soluble SPs composed of three types of QDs. The SPs can be fabricated to emit pure colors as well as a broad white light spectrum (or anything in between) that can be fine-tuned via the NC composition of the SPs. The bright emission from individual SPs is stable over time and does not blink. Such SPs hold promise as phosphors in LEDs for lighting, opto-electrical integration in semiconductor chips and as biological labels.
Methods
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Synthesis of QDs
Three different populations of Cd(Se,ZnS) core/(Cd,Zn,S) shell QDs emitting in different regions of the visible spectrum were synthesized according to a modified literature procedure. (35-37) For further details about the synthesis and characterization procedure see the Supporting Information. The QDs were precipitated by centrifugation with the addition of a MeOH:BuOH 3:1 v/v solution and redispersed in cyclohexane to form stock solutions with a concentration of 8–15 mg/mL.
Synthesis of SPs
For the SPs, the three different solutions of core/shell QDs were mixed in the desired ratio to a total volume of 1 mL and then mixed with 10 mL water containing sodium dodecyl sulfate and dextran. The mixture was sheared at a shear rate of 7 × 103 s–1 in a shear cell with a gap of 0.1 mm, and the resulting oil-in-water emulsion was heated at 68 °C for 4 h. The resulting SPs were precipitated by centrifugation, and the supernatant, containing surfactants and dextran in excess, was discarded. SPs were redispersed in deionized water. For a detailed description of the methods and equipment used, see the Supporting Information.
Electron Microscopy
HAADF-STEM images, SE-STEM images, EDS maps, and electron tomography series of the SPs were acquired using a FEI Osiris and a FEI Tecnai electron microscopes operated at 200 kV. Electron tomography series were acquired by using a Fischione model 2020 single tilt tomography holder. The series were acquired within the tilt ranges from −64° to +74° and from −76° to +64° and a tilt increment of 2°. For the reconstruction of the series, the simultaneous iterative reconstruction technique (SIRT) was used, implemented in the ASTRA toolbox. (38-40)
HAADF-STEM images and EDS maps of the QDs were acquired using an aberration-corrected “cubed” FEI Titan 60–300 electron microscope operated at 120 kV, equipped with a ChemiSTEM (41) system.
Supporting Information
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The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsnano.7b03975.
Synthesis of core/multishell QDs, optical characterization of the QDs, synthesis of the SPs, determination of the quantum yield of QDs and SPs, determination of the RDF and CIE coordinates (PDF)
Terms & Conditions
Most electronic Supporting Information files are available without a subscription to ACS Web Editions. Such files may be downloaded by article for research use (if there is a public use license linked to the relevant article, that license may permit other uses). Permission may be obtained from ACS for other uses through requests via the RightsLink permission system: http://pubs.acs.org/page/copyright/permissions.html.
Author Information
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- Daniel Vanmaekelbergh - †Condensed Matter and Interfaces and ‡Soft Condensed Matter, Debye Institute for Nanomaterials Science, Utrecht University, P.O. Box 80000, 3508 TA Utrecht, The Netherlands; EMAT, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium;http://orcid.org/0000-0002-3535-8366;
- Sara Bals - EMAT, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium;http://orcid.org/0000-0002-4249-8017
Acknowledgment
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We thank J. J. Geuchies for help with the optical analysis, W. Vlug for providing silica particles filled with RITC, J. D. Meeldijk for his assistance with SE-STEM measurements, E. B. van der Wee for help with the calculation of the radial distribution functions, and M. van Huis and S. Dussi for very fruitful discussions. This work was supported by the European Comission via the Marie-Sklodowska Curie action Phonsi (H2020-MSCA-ITN-642656). D.V. wishes to thank the Dutch FOM (program DDC13), NWO–CW (Toppunt 718.015.002), and the European Research Council under HORIZON 2020 (grant 692691 FIRSTSTEP) for financial support. A.v.B. and F.M. acknowledge partial funding from the European Research Council under the European Union’s Seventh Framework Programme (FP-2007-2013)/ERC advanced grant agreement 291667: HierarSACol. S.B. and D.Z. acknowledge financial support from the European Research Council (starting grant no. COLOURATOM 335078), and T.A. acknowledges funding from the Research Foundation Flanders (FWO, Belgium) through a postdoctoral grant.
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- 4Christodoulou, S.; Vaccaro, G.; Pinchetti, V.; De Donato, F.; Grim, J. Q.; Casu, a.; Genovese, a.; Vicidomini, G.; Diaspro, a.; Brovelli, S.; Manna, L.; Moreels, I. Synthesis of Highly Luminescent Wurtzite CdSe/CdS Giant-Shell Nanocrystals Using a Fast Continuous Injection Route J. Mater. Chem. C 2014, 2, 3439 DOI: 10.1039/c4tc00280f[Crossref], [CAS], Google Scholar4https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXlsFyrurY%253D&md5=dbc871782c730e500e58f0178f98ebedSynthesis of highly luminescent wurtzite CdSe/CdS giant-shell nanocrystals using a fast continuous injection routeChristodoulou, S.; Vaccaro, G.; Pinchetti, V.; De Donato, F.; Grim, J. Q.; Casu, A.; Genovese, A.; Vicidomini, G.; Diaspro, A.; Brovelli, S.; Manna, L.; Moreels, I.Journal of Materials Chemistry C: Materials for Optical and Electronic Devices (2014), 2 (17), 3439-3447CODEN: JMCCCX; ISSN:2050-7534. (Royal Society of Chemistry)We synthesized CdSe/CdS giant-shell nanocrystals, with a CdSe core diam. between 2.8 nm and 5.5 nm, and a CdS shell thickness of up to 7-8 nm (equiv. to about 20 monolayers of CdS). Both the core and shell have a wurtzite crystal structure, yielding epitaxial growth of the shell and nearly defect-free crystals. As a result, the photoluminescence (PL) quantum efficiency (QE) is as high as 90%. Quant. PL measurements at various excitation wavelengths allow us to sep. the nonradiative decay into contributions from interface and surface trapping, giving us pathways for future optimization of the structure. In addn., the NCs do not blink, and the giant shell and concurring strong electron delocalization efficiently suppress Auger recombination, yielding a biexciton lifetime of about 15 ns. The corresponding biexciton PL QE equals 11% in 5.5/18.1 nm CdSe/CdS. Variable-temp. time-resolved PL and PL under magnetic fields further reveal that the emission at cryogenic temp. originates from a neg. trion-state, in agreement with other CdSe/CdS giant-shell systems reported in the literature.
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- 6García-Santamaría, F.; Chen, Y.; Vela, J.; Schaller, R. D.; Hollingsworth, J. a; Klimov, V. Suppressed Auger Recombination in “Giant” Nanocrystals Boosts Optical Gain Performance Nano Lett. 2009, 9, 3482– 3488 DOI: 10.1021/nl901681d[ACS Full Text], [CAS], Google Scholar6https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXmvV2ktLg%253D&md5=b5f611debf8ea310425d554049de1950Suppressed Auger Recombination in "Giant" Nanocrystals Boosts Optical Gain PerformanceGarcia-Santamaria, Florencio; Chen, Yongfen; Vela, Javier; Schaller, Richard D.; Hollingsworth, Jennifer A.; Klimov, Victor I.Nano Letters (2009), 9 (10), 3482-3488CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)Many potential applications of semiconductor nanocrystals are hindered by nonradiative Auger recombination wherein the electron-hole (exciton) recombination energy is transferred to a 3rd charge carrier. This process severely limits the lifetime and bandwidth of optical gain, leads to large nonradiative losses in light-emitting diodes and photovoltaic cells, and is believed to be responsible for intermittency (blinking) of emission from single nanocrystals. The development of nanostructures in which Auger recombination is suppressed has recently been the subject of much research in the colloidal nanocrystal field. Here, the authors provide direct exptl. evidence that so-called giant nanocrystals consisting of a small CdSe core and a thick CdS shell exhibit a significant (orders of magnitude) suppression of Auger decay rates. As a consequence, even multiexcitons of a very high order exhibit significant emission efficiencies, which allows the authors to demonstrate optical amplification with an extraordinarily large bandwidth (>500 meV) and record low excitation thresholds. This demonstration represents an important milestone toward practical lasing technologies using soln.-processable colloidal nanoparticles.
- 7Mahler, B.; Spinicelli, P.; Buil, S.; Quelin, X.; Hermier, J.-P.; Dubertret, B. Towards Non-Blinking Colloidal Quantum Dots Nat. Mater. 2008, 7, 659– 664 DOI: 10.1038/nmat2222[Crossref], [PubMed], [CAS], Google Scholar7https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXovFWrt7c%253D&md5=51fcba04adc6f1aaecb939dd1cbbd8e7Towards non-blinking colloidal quantum dotsMahler, Benoit; Spinicelli, Piernicola; Buil, Stephanie; Quelin, Xavier; Hermier, Jean-Pierre; Dubertret, BenoitNature Materials (2008), 7 (8), 659-664CODEN: NMAACR; ISSN:1476-1122. (Nature Publishing Group)At a single-mol. level, fluorophore emission intensity fluctuates between bright and dark states. These fluctuations, known as blinking, limit the use of fluorophores in single-mol. expts. The dark-state duration shows a universal heavy-tailed power-law distribution characterized by the occurrence of long nonemissive periods. Novel CdSe-CdS core-shell quantum dots were synthesized with thick cryst. shells, 68% of which do not blink when obsd. individually at 33 Hz for 5 min. A direct correlation was established between shell thickness and blinking occurrences. The statistics of dark periods that appear at high acquisition rates (1 kHz) are not heavy tailed, in striking contrast with previous observations. Blinking statistics are thus not as universal as thought so far. It is anticipated that the results will help to better understand the physicochem. of single-fluorophore emission and rationalize the design of other fluorophores that do not blink.
- 8Hollingsworth, J. A. Heterostructuring Nanocrystal Quantum Dots toward Intentional Suppression of Blinking and Auger Recombination Chem. Mater. 2013, 25, 1318– 1331 DOI: 10.1021/cm304161d[ACS Full Text], [CAS], Google Scholar8https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXjsFaru74%253D&md5=995b022a3909f6950136590b5e6f7f5bHeterostructuring Nanocrystal Quantum Dots Toward Intentional Suppression of Blinking and Auger RecombinationHollingsworth, Jennifer A.Chemistry of Materials (2013), 25 (8), 1318-1331CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)A review. At the level of a single particle, nanocrystal quantum dots (NQDs) fluoresce intermittently or blink. They are also characterized by an efficient nonradiative recombination process known as Auger recombination (AR). Recently, new approaches to NQD heterostructuring were developed that directly impact both blinking and AR, resulting in dramatic suppression of these unwanted processes. The 3 successful hetero-NQD motifs are reviewed here: (1) interfacial alloying, (2) thick or giant shells, and (3) specific type-II electronic structures. These approaches, which rely on modifying or tuning internal NQD core/shell structures, are compared with alternative strategies for blinking suppression that rely, instead, on surface modifications or surface-mediated interactions. Finally, in each case, the unique synthetic approaches or challenges addressed that have driven the realization of novel and important functionality are discussed, along with the implications for development of a comprehensive materials design strategy for blinking and AR-suppressed heterostructured NQDs.
- 9Park, Y.-S.; Bae, W. K.; Baker, T.; Lim, J.; Klimov, V. I. Effect of Auger Recombination on Lasing in Heterostructured Quantum Dots with Engineered Core/Shell Interfaces Nano Lett. 2015, 15, 7319– 7328 DOI: 10.1021/acs.nanolett.5b02595[ACS Full Text], [CAS], Google Scholar9https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhsFCjurjF&md5=3132d3f8924b469db45cf84639d33401Effect of Auger Recombination on Lasing in Heterostructured Quantum Dots with Engineered Core/Shell InterfacesPark, Young-Shin; Bae, Wan Ki; Baker, Thomas; Lim, Jaehoon; Klimov, Victor I.Nano Letters (2015), 15 (11), 7319-7328CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)Nanocrystal quantum dots (QDs) are attractive materials for applications as laser media because of their bright, size-tunable emission and the flexibility afforded by colloidal synthesis. Nonradiative Auger recombination hampers optical amplification in QDs by rapidly depleting the population of gain-active multiexciton states. To elucidate the role of Auger recombination in QD lasing and isolate its influence from other factors that might affect optical gain, 2 types of CdSe/CdS core/shell QDs with the same core radii and the same total sizes but different properties of the core/shell interface (sharp vs. smooth) were studied. These samples exhibit distinctly different biexciton Auger lifetimes but are otherwise virtually identical. The suppression of Auger recombination in the sample with a smooth (alloyed) interface results in a notable improvement in the optical gain performance manifested in the redn. of the threshold for amplified spontaneous emission and the ability to produce dual-color lasing involving both the band-edge (1S) and the higher-energy (1P) electronic states. The authors develop a model, which explicitly accounts for the multiexciton nature of optical gain in QDs, and use it to analyze the competition between stimulated emission from multiexcitons and their decay via Auger recombination. These studies reemphasize the importance of Auger recombination control for the realization of real-life QD-based lasing technols. and offer practical strategies for suppression of Auger recombination via interface engineering in core/shell structures.
- 10Klimov, V. I.; Mikhailovsky, a. a.; Xu, S.; Malko, a; Hollingsworth, J. a.; Leatherdale, C. a; Eisler, H.-J.; Bawendi, M. G. Optical Gain and Stimulated Emission in Nanocrystal Quantum Dots Science (Washington, DC, U. S.) 2000, 290, 314– 317 DOI: 10.1126/science.290.5490.314[Crossref], [PubMed], [CAS], Google Scholar10https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3cXnsVGisL0%253D&md5=9cf79ab10ed1fb0ce212182066c89b62Optical gain and stimulated emission in nanocrystal quantum dotsKlimov, V. I.; Mikhailovsky, A. A.; Xu, Su; Malko, A.; Hollingsworth, J. A.; Leatherdale, C. A.; Eisler, H.-J.; Bawendiz, M. G.Science (Washington, D. C.) (2000), 290 (5490), 314-317CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)The development of optical gain in chem. synthesized semiconductor nanoparticles (nanocrystal quantum dots) has been intensely studied as the first step toward nanocrystal quantum dot lasers. The authors examd. the competing dynamical processes involved in optical amplification and lasing in nanocrystal quantum dots and found that, despite a highly efficient intrinsic nonradiative Auger recombination, large optical gain can be developed at the wavelength of the emitting transition for close-packed solids of these dots. Narrow-band stimulated emission with a pronounced gain threshold at wavelengths tunable with the size of the nanocrystal was obsd., as expected from quantum confinement effects. These results unambiguously demonstrate the feasibility of nanocrystal quantum dot lasers.
- 11Klimov, V. Spectral and Dynamical Properties of Multiexcitons in Semiconductor Nanocrystals Annu. Rev. Phys. Chem. 2007, 58, 635– 673 DOI: 10.1146/annurev.physchem.58.032806.104537[Crossref], [PubMed], [CAS], Google Scholar11https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXlslSitL4%253D&md5=255b3af2784714c438097359fb36d2b6Spectral and dynamical properties of multiexcitons in semiconductor nanocrystalsKlimov, Victor I.Annual Review of Physical Chemistry (2007), 58 (), 635-673CODEN: ARPLAP; ISSN:0066-426X. (Annual Reviews Inc.)A review. Because of the strong spatial confinement of electronic wave functions and reduced dielec. screening, the effects of carrier-carrier Coulomb interactions are greatly enhanced in semiconductor nanocrystals (NCs) compared with those in bulk materials. These interactions open a highly efficient decay channel via Auger recombination, which represents a dominant recombination pathway for multiexcitons in NCs. Also, strong Coulomb coupling between charge carriers leads to extremely efficient direct photogeneration of multiexcitons by single photons via carrier (or exciton) multiplication. This review focuses on spectral and dynamical properties of multiexcitons in semiconductor NCs. The specific topics discussed here include the structure of NC electronic states, spectral signatures of multiexcitons in transient absorption and photoluminescence, exciton-exciton interaction energies, Auger recombination, and carrier multiplication. This chapter also briefly reviews the implications of multiexciton effects for practical technologies, such as NC lasing and photovoltaics.
- 12Alivisatos, P. The Use of Nanocrystals in Biological Detection Nat. Biotechnol. 2004, 22, 47– 52 DOI: 10.1038/nbt927[Crossref], [PubMed], [CAS], Google Scholar12https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2cXls1el&md5=aeee2f2da13dd07d0f013808b045f925The use of nanocrystals in biological detectionAlivisatos, PaulNature Biotechnology (2004), 22 (1), 47-52CODEN: NABIF9; ISSN:1087-0156. (Nature Publishing Group)A review. In the coming decade, the ability to sense and detect the state of biol. systems and living organisms optically, elec. and magnetically will be radically transformed by developments in materials physics and chem. The emerging ability to control the patterns of matter on the nanometer length scale can be expected to lead to entirely new types of biol. sensors. These new systems will be capable of sensing at the single-mol. level in living cells, and capable of parallel integration for detection of multiple signals, enabling a diversity of simultaneous expts., as well as better crosschecks and controls.
- 13Bruchez, M., Jr.; Moronne, M.; Gin, P.; Weiss, S.; Alivisatos, A. P. Semiconductor Nanocrystals as Fluorescent Biological Labels Science 1998, 281, 2013– 2016 DOI: 10.1126/science.281.5385.2013[Crossref], [PubMed], [CAS], Google Scholar13https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1cXmtlKgurw%253D&md5=db36fdbbfbc2facf264c3f98c1c8efcbSemiconductor nanocrystals as fluorescent biological labelsBruchez, Marcel, Jr.; Moronne, Mario; Gin, Peter; Weiss, Shimon; Alivisatos, A. PaulScience (Washington, D. C.) (1998), 281 (5385), 2013-2016CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)Semiconductor nanocrystals were prepd. for use as fluorescent probes in biol. staining and diagnostics. Compared with conventional fluorophores, the nanocrystals have a narrow, tunable, sym. emission spectrum and are photochem. stable. The advantages of the broad, continuous excitation spectrum were demonstrated in a dual-emission, single-excitation labeling expt. on mouse fibroblasts. These nanocrystal probes are thus complementary and in some cases may be superior to existing fluorophores.
- 14Michalet, X.; Pinaud, F.; Bentolila, L.; Tsay, J.; Doose, S.; Li, J.; Sundaresan, G.; Wu, A.; Gambhir, S.; Weiss, S. Quantum Dots for Live Cells, in Vivo Imaging, and Diagnostics Science (Washington, DC, U. S.) 2005, 307, 538– 544 DOI: 10.1126/science.1104274[Crossref], [PubMed], [CAS], Google Scholar14https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2MXmslOhtw%253D%253D&md5=03a28864cfd8c3c4269cc9919d1eafb9Quantum Dots for Live Cells, in Vivo Imaging, and DiagnosticsMichalet, X.; Pinaud, F. F.; Bentolila, L. A.; Tsay, J. M.; Doose, S.; Li, J. J.; Sundaresan, G.; Wu, A. M.; Gambhir, S. S.; Weiss, S.Science (Washington, DC, United States) (2005), 307 (5709), 538-544CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)A review. Research on fluorescent semiconductor nanocrystals (also known as quantum dots or qdots) has evolved over the past two decades from electronic materials science to biol. applications. We review current approaches to the synthesis, solubilization, and functionalization of qdots and their applications to cell and animal biol. Recent examples of their exptl. use include the observation of diffusion of individual glycine receptors in living neurons and the identification of lymph nodes in live animals by near-IR emission during surgery. The new generations of qdots have far-reaching potential for the study of intracellular processes at the single-mol. level, high-resoln. cellular imaging, long-term in vivo observation of cell trafficking, tumor targeting, and diagnostics.
- 15Meinardi, F.; McDaniel, H.; Carulli, F.; Colombo, A.; Velizhanin, K. a.; Makarov, N. S.; Simonutti, R.; Klimov, V. I.; Brovelli, S. Highly Efficient Large-Area Colourless Luminescent Solar Concentrators Using Heavy-Metal-Free Colloidal Quantum Dots Nat. Nanotechnol. 2015, 10, 878– 885 DOI: 10.1038/nnano.2015.178[Crossref], [PubMed], [CAS], Google Scholar15https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhtlyls7vO&md5=b63662c4e01349d552589031b5cc71deHighly efficient large-area colorless luminescent solar concentrators using heavy-metal-free colloidal quantum dotsMeinardi, Francesco; McDaniel, Hunter; Carulli, Francesco; Colombo, Annalisa; Velizhanin, Kirill A.; Makarov, Nikolay S.; Simonutti, Roberto; Klimov, Victor I.; Brovelli, SergioNature Nanotechnology (2015), 10 (10), 878-885CODEN: NNAABX; ISSN:1748-3387. (Nature Publishing Group)Luminescent solar concentrators serving as semitransparent photovoltaic windows could become an important element in net zero energy consumption buildings of the future. Colloidal quantum dots are promising materials for luminescent solar concentrators as they can be engineered to provide the large Stokes shift necessary for suppressing reabsorption losses in large-area devices. Existing Stokes-shift-engineered quantum dots allow for only partial coverage of the solar spectrum, which limits their light-harvesting ability and leads to coloring of the luminescent solar concentrators, complicating their use in architecture. Here, we use quantum dots of ternary I-III-VI2 semiconductors to realize the first large-area quantum dot-luminescent solar concentrators free of toxic elements, with reduced reabsorption and extended coverage of the solar spectrum. By incorporating CuInSexS2-x quantum dots into photo-polymd. poly(lauryl methacrylate), we obtain freestanding, colorless slabs that introduce no distortion to perceived colors and are thus well suited for the realization of photovoltaic windows. Thanks to the suppressed reabsorption and high emission efficiencies of the quantum dots, we achieve an optical power efficiency of 3.2%. Ultrafast spectroscopy studies suggest that the Stokes-shifted emission involves a conduction-band electron and a hole residing in an intragap state assocd. with a native defect.
- 16Meinardi, F.; Colombo, A.; Velizhanin, K. a.; Simonutti, R.; Lorenzon, M.; Beverina, L.; Viswanatha, R.; Klimov, V.; Brovelli, S. Large-Area Luminescent Solar Concentrators Based on “Stokes-Shift-Engineered” Nanocrystals in a Mass-Polymerized PMMA Matrix Nat. Photonics 2014, 8, 392– 399 DOI: 10.1038/nphoton.2014.54[Crossref], [CAS], Google Scholar16https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXmtlWqsbg%253D&md5=cfa9667bf689b3f506ee0c26368f98efLarge-area luminescent solar concentrators based on 'Stokes-shift-engineered' nanocrystals in a mass-polymerized PMMA matrixMeinardi, Francesco; Colombo, Annalisa; Velizhanin, Kirill A.; Simonutti, Roberto; Lorenzon, Monica; Beverina, Luca; Viswanatha, Ranjani; Klimov, Victor I.; Brovelli, SergioNature Photonics (2014), 8 (5), 392-399CODEN: NPAHBY; ISSN:1749-4885. (Nature Publishing Group)Luminescent solar concentrators are cost-effective complements to semiconductor photovoltaics that can boost the output of solar cells and allow for the integration of photovoltaic-active architectural elements into buildings (for example, photovoltaic windows). Colloidal quantum dots are attractive for use in luminescent solar concentrators, but their small Stokes shift results in reabsorption losses that hinder the realization of large-area devices. Here, we use 'Stokes-shift-engineered' CdSe/CdS quantum dots with giant shells (giant quantum dots) to realize luminescent solar concentrators without reabsorption losses for device dimensions up to tens of centimeters. Monte-Carlo simulations show a 100-fold increase in efficiency using giant quantum dots compared with core-only nanocrystals. We demonstrate the feasibility of this approach by using high-optical-quality quantum dot-polymethylmethacrylate nanocomposites fabricated using a modified industrial method that preserves the light-emitting properties of giant quantum dots upon incorporation into the polymer. Study of these luminescent solar concentrators yields optical efficiencies >10% and an effective concn. factor of 4.4. These results demonstrate the significant promise of Stokes-shift-engineered quantum dots for large-area luminescent solar concentrators.
- 17Bradshaw, L. R.; Knowles, K. E.; McDowall, S.; Gamelin, D. R. Nanocrystals for Luminescent Solar Concentrators Nano Lett. 2015, 15, 1315– 1323 DOI: 10.1021/nl504510t[ACS Full Text], [CAS], Google Scholar17https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXmvFSntA%253D%253D&md5=66c24439a8954a8aa26bff77aca40fe7Nanocrystals for Luminescent Solar ConcentratorsBradshaw, Liam R.; Knowles, Kathryn E.; McDowall, Stephen; Gamelin, Daniel R.Nano Letters (2015), 15 (2), 1315-1323CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)Luminescent solar concentrators (LSCs) harvest sunlight over large areas and conc. this energy onto photovoltaics or for other uses by transporting photons through macroscopic waveguides. Although attractive for lowering solar energy costs, LSCs remain severely limited by luminophore reabsorption losses. Here, the authors report a quant. comparison of 4 types of nanocrystal (NC) phosphors recently proposed to minimize reabsorption in large-scale LSCs: 2 nanocrystal heterostructures and 2 doped nanocrystals. Exptl. and numerical analyses both show that even the small core absorption of the leading NC heterostructures causes major reabsorption losses at relatively short transport lengths. Doped NCs outperform the heterostructures substantially in this crit. property. A new LSC phosphor is introduced, nanocryst. Cd1-xCuxSe, that outperforms all other leading NCs by a significant margin in both small- and large-scale LSCs under full-spectrum conditions.
- 18Shirasaki, Y.; Supran, G. J.; Bawendi, M. G.; Bulović, V. Emergence of Colloidal Quantum-Dot Light-Emitting Technologies Nat. Photonics 2013, 7, 13– 23 DOI: 10.1038/nphoton.2012.328[Crossref], [CAS], Google Scholar18https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XhvV2ntLfI&md5=9ce4673b68f86faa7c83212c053193c4Emergence of colloidal quantum-dot light-emitting technologiesShirasaki, Yasuhiro; Supran, Geoffrey J.; Bawendi, Moungi G.; Bulovic, VladimirNature Photonics (2013), 7 (1), 13-23CODEN: NPAHBY; ISSN:1749-4885. (Nature Publishing Group)A review. Since their inception 18 years ago, elec. driven colloidal quantum-dot light-emitting devices (QD-LEDs) have increased in external quantum efficiency from less than 0.01% to around 18%. The high luminescence efficiency and uniquely size-tunable color of soln.-processable semiconducting colloidal QDs highlight the potential of QD-LEDs for use in energy-efficient, high-color-quality thin-film display and solid-state lighting applications. Indeed, last year saw the first demonstrations of elec. driven full-color QD-LED displays, which foreshadow QD technologies that will transcend the optically excited QD-enhanced lighting products already available today. We here discuss the key advantages of using QDs as luminophores in LEDs and outline the operating mechanisms of four types of QD-LED. State-of-the-art visible-wavelength LEDs and the promise of near-IR and heavy-metal-free devices are also highlighted. As QD-LED efficiencies approach those of mol. org. LEDs, we identify the key scientific and technol. challenges facing QD-LED commercialization and offer our outlook for on-going strategies to overcome these challenges.
- 19Kim, J.-H.; Jo, D.-Y.; Lee, K.-H.; Jang, E.-P.; Han, C.-Y.; Jo, J.-H.; Yang, H. White Electroluminescent Lighting Device Based on a Single Quantum Dot Emitter Adv. Mater. 2016, 28, 5093– 5098 DOI: 10.1002/adma.201600815[Crossref], [PubMed], [CAS], Google Scholar19https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XntFCgtbg%253D&md5=c25062f2d1998f2b0e0d12c98c13ece5White Electroluminescent Lighting Device Based on a Single Quantum Dot EmitterKim, Jong-Hoon; Jo, Dae-Yeon; Lee, Ki-Heon; Jang, Eun-Pyo; Han, Chang-Yeol; Jo, Jung-Ho; Yang, HeesunAdvanced Materials (Weinheim, Germany) (2016), 28 (25), 5093-5098CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)Cu/Ga ratio-varied Cu-Ga-S (CGS)/ZnS quantum dots (QDs) were synthesized, finding that Cu deficiency played crit. roles in controlling their absorption and luminescence (PL) properties and that the nominal ratio of Cu/Ga = 1/8 was the most suitable in securing the widest visible coverage toward white emission as well as high QY. The highest QY ≤76% was achievable by further adjusting the ZnS-shelling period of Cu/Ga = 1.8 based QDs. Using the resulting QDs, single QD-based white QD-based LED (QLED) with a multilayered sequence of PVK hole transport layer (HTL), CGS/ZnS QD emitting layer (EML), and ZnO nanoparticle (NP) electron transport layer (ETL) was fabricated via all-soln. processing. White electroluminescence (EL) that originated only from QDs without any contribution of charge transport layer (CTL) emissions could be obtained of exclusive exciton recombination at EML. Obsd. field-dependent EL spectral variation, showing a steady redn. of low energy EL relative intensity vs. high energy 1 with increasing voltage, was explained jointly with respect to excited-state lifetime and thermal quenching behaviors between DAP vs. CB-to-VCu transitions. Compared to non-Cd QD-based, white EL-capable devices reported so far, the present white QLED that possessed satisfactorily high CRIs of 83-88 exhibited the record EL quantities of 1007 cd m-2 in luminance, 3.6 cd A-1 in current efficiency, 1.91 m W-1 in power efficiency, and 1.9% in EQE. Addnl. fabrication of a white flexible planar QLED and a warm white EL-capable device was fulfilled.
- 20Panda, S. K.; Hickey, S. G.; Demir, H. V.; Eychmüller, A. Bright White-Light Emitting Manganese and Copper Co-Doped ZnSe Quantum Dots Angew. Chem. 2011, 123, 4524– 4528 DOI: 10.1002/ange.201100464
- 21Schreuder, M. A.; Xiao, K.; Ivanov, I. N.; Weiss, S. M.; Rosenthal, S. J. White Light-Emitting Diodes Based on Ultrasmall CdSe Nanocrystal Electroluminescence Nano Lett. 2010, 10, 573– 576 DOI: 10.1021/nl903515g[ACS Full Text], [CAS], Google Scholar21https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXjs1yrtQ%253D%253D&md5=6fe53aab794215002cb68ace8bb525e1White Light-Emitting Diodes Based on Ultrasmall CdSe Nanocrystal ElectroluminescenceSchreuder, Michael A.; Xiao, Kai; Ivanov, Ilia N.; Weiss, Sharon M.; Rosenthal, Sandra J.Nano Letters (2010), 10 (2), 573-576CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)We report white light-emitting diodes fabricated with ultrasmall CdSe nanocrystals, which demonstrate electroluminescence from a size of nanocrystals (<2 nm) previously thought to be unattainable. These LEDs have excellent color characteristics, defined by their pure white CIE color coordinates (0.333, 0.333), correlated color temps. of 5461-6007 K, and color rendering indexes as high as 96.6. The effect of high voltage on the trap states responsible for the white emission is also described.
- 22Bowers, M. M. J.; Ii, M. J. B.; McBride, J. R.; Rosenthal, S. J. White-Light Emission from Magic-Sized Cadmium Selenide Nanocrystals J. Am. Chem. Soc. 2005, 127, 15378– 15379 DOI: 10.1021/ja055470d[ACS Full Text], [CAS], Google Scholar22https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2MXhtFWku7nK&md5=1d3b549fa9a783179bf140812db28957White-Light Emission from Magic-Sized Cadmium Selenide NanocrystalsBowers, Michael J., II; McBride, James R.; Rosenthal, Sandra J.Journal of the American Chemical Society (2005), 127 (44), 15378-15379CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Magic-sized Cd selenide (CdSe) nanocrystals were pyrolytically synthesized. These ultra-small nanocrystals exhibit broadband emission (420-710 nm) that covers most of the visible spectrum while not suffering from self absorption. This behavior is a direct result of the extremely narrow size distribution and unusually large Stokes shift (40-50 nm). The intrinsic properties of these ultra-small nanocrystals make them an ideal material for applications in solid state lighting and also the perfect platform to study the mol.-to-nanocrystal transition.
- 23Nasilowski, M.; Spinicelli, P.; Patriarche, G.; Dubertret, B. Gradient CdSe/CdS Quantum Dots with Room Temperature Biexciton Unity Quantum Yield Nano Lett. 2015, 15, 3953– 3958 DOI: 10.1021/acs.nanolett.5b00838[ACS Full Text], [CAS], Google Scholar23https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXosFGrsr4%253D&md5=eae70bffa7e67747474be7964d57e964Gradient CdSe/CdS Quantum Dots with Room Temperature Biexciton Unity Quantum YieldNasilowski, Michel; Spinicelli, Piernicola; Patriarche, Gilles; Dubertret, BenoitNano Letters (2015), 15 (6), 3953-3958CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)Auger recombination is a major limitation for the fluorescent emission of quantum dots (QDs). It is the main source of QDs fluorescence blinking at the single-particle level. At high-power excitation, when several charge carriers are formed inside a QD, Auger becomes more efficient and severely decreases the quantum yield (QY) of multiexcitons. This limits the efficiency and the use of colloidal QDs in applications where intense light output is required. Here, the authors present a new generation of thick-shell CdSe/CdS QDs with dimensions >40 nm and a compn. gradient between the core and the shell that exhibits 100% QY for the emission of both the monoexciton and the biexciton in air and at room temp. for all the QDs the authors obsd. The fluorescence emission of these QDs is perfectly Poissonian at the single-particle level at different excitation levels and temps., from 30 to 300 K. In these QDs, the emission of high-order (>2) multiexcitons is quite efficient, and the authors observe white light emission at the single-QD level when high excitation power is used. These gradient thick shell QDs confirm the suppression of Auger recombination in gradient core/shell structures and help further establish the colloidal QDs with a gradient shell as a very stable source of light even under high excitation.
- 24Brovelli, S.; Bae, W. K.; Galland, C.; Giovanella, U.; Meinardi, F.; Klimov, V. I. Dual-Color Electroluminescence from Dot-in-Bulk Nanocrystals Nano Lett. 2014, 14, 486– 494 DOI: 10.1021/nl403478s[ACS Full Text], [CAS], Google Scholar24https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhvFejtb7E&md5=9740809fba78d005bc31747890216a00Dual-Color Electroluminescence from Dot-in-Bulk NanocrystalsBrovelli, Sergio; Bae, Wan Ki; Galland, Christophe; Giovanella, Umberto; Meinardi, Francesco; Klimov, Victor I.Nano Letters (2014), 14 (2), 486-494CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)The emission color from colloidal semiconductor nanocrystals (NCs) is usually tuned through control of particle size, while multicolor emission is obtained by mixing NCs of different sizes within an emissive layer. Here, we demonstrate that recently introduced "dot-in-bulk" (DiB) nanocrystals can emit two-color light under both optical excitation and elec. injection. We show that the effective emission color can be controlled by adjusting the relative amplitudes of the core and shell emission bands via the intensity of optical excitation or applied bias in the cases of photoluminescence (PL) and electroluminescence (EL), resp. To investigate the role of nonradiative carrier losses due to trapping at intragap states, we incorporate DiB NCs into functional light-emitting diodes and study their PL as a function of applied bias below the EL excitation threshold. We show that voltage-dependent changes in core and shell emissions are not due to the applied elec. field but rather arise from the transfer of charges between the anode and the NC intragap trap sites. The changes in the occupancy of trap states can be described in terms of the raising (lowering) of the Fermi level for reverse (direct) bias. We find that the applied voltage affects the overall PL intensity primarily via the electron-trapping channel while bias-induced changes in hole-trapping play a less significant role, limited to a weak effect on core emission.
- 25Lee, K.; Han, C.; Kang, H.; Ko, H.; Lee, C.; Lee, J.; Myoung, N.; Yim, S.-Y.; Yang, H. Highly Efficient, Color-Reproducible Full-Color Electroluminescent Devices Based on Red/Green/Blue Quantum Dot-Mixed Multilayer ACS Nano 2015, 9, 10941– 10949 DOI: 10.1021/acsnano.5b05513[ACS Full Text], [CAS], Google Scholar25https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhs1SisL3E&md5=86c660298c2fa977b5e23fd67eedb656Highly Efficient, Color-Reproducible Full-Color Electroluminescent Devices Based on Red/Green/Blue Quantum Dot-Mixed MultilayerLee, Ki-Heon; Han, Chang-Yeol; Kang, Hee-Don; Ko, Heejoo; Lee, Changho; Lee, Jonghyuk; Myoung, NoSoung; Yim, Sang-Youp; Yang, HeesunACS Nano (2015), 9 (11), 10941-10949CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)Over the past few years the performance of colloidal quantum dot-light-emitting diode (QLED) was progressively improved. Most of QLED work was fulfilled as monochromatic device, while full-color-enabling white QLED still remains nearly unexplored. Using red, green, and blue quantum dots (QDs), bichromatic and trichromatic QLEDs were fabricated through sequential soln.-processed deposition of poly(9-vinlycarbazole) (PVK) hole transport layer, 2 or 3 types of QDs-mixed multilayer, and ZnO nanoparticle electron transport layer. The relative electroluminescent (EL) spectral ratios of constituent QDs in the above multicolored devices inevitably vary with applied bias, leading to the common observation of an increasing contribution of a higher-band gap QD EL over low-band gap 1 at a higher voltage. The white EL from a trichromatic device is resolved into its primary colors through combining with color filters, producing an exceptional color gamut of 126% relative to National Television Systems Committee (NTSC) color space that a state-of-the-art full-color org. LED counterpart cannot attain. The trichromatic white QLED also displays the record-high EL performance such as the peak values of 23,352 cd/m2 in luminance, 21.8 cd/A in current efficiency, and 10.9% in external quantum efficiency.
- 26de Nijs, B.; Dussi, S.; Smallenburg, F.; Meeldijk, J. D.; Groenendijk, D. J.; Filion, L.; Imhof, A.; Dijkstra, M.; Van Blaaderen, A. Entropy-Driven Formation of Large Icosahedral Colloidal Clusters by Spherical Confinement Nat. Mater. 2015, 14, 56– 60 DOI: 10.1038/nmat4072[Crossref], [PubMed], [CAS], Google Scholar26https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhsVCrtLfJ&md5=f3d69b41b0a61150dc3b03cc3c9d1945Entropy-driven formation of large icosahedral colloidal clusters by spherical confinementde Nijs, Bart; Dussi, Simone; Smallenburg, Frank; Meeldijk, Johannes D.; Groenendijk, Dirk J.; Filion, Laura; Imhof, Arnout; van Blaaderen, Alfons; Dijkstra, MarjoleinNature Materials (2015), 14 (1), 56-60CODEN: NMAACR; ISSN:1476-1122. (Nature Publishing Group)Icosahedral symmetry, which is not compatible with truly long-range order, can be found in many systems, such as liqs., glasses, at. clusters, quasicrystals, and virus-capsids. To obtain arrangements with a high degree of icosahedral order from tens of particles or more, interparticle attractive interactions are considered to be essential. The authors report that entropy and spherical confinement suffice for the formation of icosahedral clusters consisting of up to 100,000 particles. Specifically, by using real-space measurements on nanometer- and micrometer-sized colloids, as well as computer simulations, the authors show that tens of thousands of hard spheres compressed under spherical confinement spontaneously crystallize into icosahedral clusters that are entropically favored over the bulk face-centered cubic crystal structure. These findings provide insights into the interplay between confinement and crystn. and into how these are connected to the formation of icosahedral structures.
- 27Vanmaekelbergh, D.; van Vugt, L. K.; Bakker, H.; Rabouw, F. T.; de Nijs, B.; van Dijk-Moes, R.; Beasjou, P.; Van Blaaderen, A. Shape-Dependent Multiexciton Emission and Whispering Gallery Modes in Supraparticles of CdSe/Multishell Quantum Dots ACS Nano 2015, 9, 3942– 3950 DOI: 10.1021/nn507310f[ACS Full Text], [CAS], Google Scholar27https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXlvV2gsbs%253D&md5=f4a45ce7db6d89782edccb5869ba568eShape-Dependent Multiexciton Emission and Whispering Gallery Modes in Supraparticles of CdSe/Multishell Quantum DotsVanmaekelbergh, Daniel; van Vugt, Lambert K.; Bakker, Henriette E.; Rabouw, Freddy T.; Nijs, Bart de; van Dijk-Moes, Relinde J. A.; van Huis, Marijn A.; Baesjou, Patrick J.; van Blaaderen, AlfonsACS Nano (2015), 9 (4), 3942-3950CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)Semiconductors are indispensable as the active light-emitting element in many optoelectronic devices. However, even the purest bulk semiconductors suffer from considerable nonradiative recombination leading to low luminescence efficiencies. Zero-dimensional quantum dots show a much better carrier-to-photon conversion caused by confinement of the excitons but suffer from nonradiative recombination when assembled into a solid, due to exciton energy transfer. Here, the authors report on the shape-dependent optical properties of self-assembled supraparticles composed of CdSe/multishell nanocrystals. All supraparticles show stable and bright luminescence in ambient up to high excitation intensities. When the supraparticles are deposited on a Si surface their spherical shape is deformed due to drying. In addn. to single-exciton emission, the authors observe bright emission from multiexciton states at high excitation powers. But supraparticles that retain their perfectly spherical shape show a spectrum with sharp Mie whispering gallery modes, while multiexciton emission is absent.
- 28Mabille, C.; Schmitt, V.; Gorria, P.; Leal Calderon, F.; Faye, V.; Deminière, B.; Bibette, J. Rheological and Shearing Conditions for the Preparation of Monodisperse Emulsions Langmuir 2000, 16, 422– 429 DOI: 10.1021/la990850w[ACS Full Text], [CAS], Google Scholar28https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1MXnsFyjsLs%253D&md5=ddcdd8e275e84b8c3304df1e3d5a1d53Rheological and shearing conditions for the preparation of monodisperse emulsionsMabille, C.; Schmitt, V.; Gorria, Ph.; Calderon, F. Leal; Faye, V.; Deminiere, B.; Bibette, J.Langmuir (2000), 16 (2), 422-429CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)Monodisperse emulsions can be obtained by shearing a crude polydisperse one. The aim was to discover the required conditions for droplet fragmentation and resulting monodispersity, independently of the chem. nature of the system. (i) the role of the initial emulsion viscoelasticity and (ii) the nature of the applied shear were examd. Taking into account these features, a large variety of monodisperse materials is shown that are easily producible in reasonable quantity.
- 29Midgley, P. a.; Weyland, M. 3D Electron Microscopy in the Physical Sciences: The Development of Z-Contrast and EFTEM Tomography Ultramicroscopy 2003, 96, 413– 431 DOI: 10.1016/S0304-3991(03)00105-0[Crossref], [PubMed], [CAS], Google Scholar29https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3sXlsVWqs7w%253D&md5=0189c27492965be8b2e562035c0416a93D electron microscopy in the physical sciences: the development of Z-contrast and EFTEM tomographyMidgley, P. A.; Weyland, M.Ultramicroscopy (2003), 96 (3-4), 413-431CODEN: ULTRD6; ISSN:0304-3991. (Elsevier Science B.V.)A review. The rapid advances in nanotechnol. and the ever decreasing size of features in the microelectronics industry brings with it the need for advanced characterization with high spatial resoln. in two and three dimensions. Stereo microscopy allows some insight into the three-dimensional nature of an object but for true quant. anal., one has to turn to tomog. as a way to reconstruct a three-dimensional object from two-dimensional projections (images). X-ray tomog. allow structures to be imaged at relatively large length scales, atom probe tomog. at the at. level. Electron tomog. offers an intermediate resoln. (of ∼1 nm) with a field of view of hundreds of nm making it ideal for the characterization of many nanoscale devices. While electron tomog. was used in the biol. sciences for >30 yr, it is only now being applied to the phys. sciences. The authors review the status of electron tomog., describe the basis behind the technique and some of the practicalities of recording and analyzing data for tomog. reconstruction, particularly in regard to solving three-dimensional problems that are encountered in materials science at the nanometer level. The authors present examples of how STEM dark-field imaging and energy-filtered TEM can be used successfully to examine nearly all types of specimens likely to be encountered by the phys. scientist.
- 30Altantzis, T.; Goris, B.; Sánchez-Iglesias, A.; Grzelczak, M.; Liz-Marzán, L. M.; Bals, S. Quantitative Structure Determination of Large Three-Dimensional Nanoparticle Assemblies Part. Part. Syst. Charact. 2013, 30, 84– 88 DOI: 10.1002/ppsc.201200045[Crossref], [CAS], Google Scholar30https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38Xhs1OgsLzO&md5=fd3d02dfb17346524ddbdc18e672b810Quantitative Structure Determination of Large Three-Dimensional Nanoparticle AssembliesAltantzis, Thomas; Goris, Bart; Sanchez-Iglesias, Ana; Grzelczak, Marek; Liz-Marzan, Luis M.; Bals, SaraParticle & Particle Systems Characterization (2013), 30 (1), 84-88CODEN: PPCHEZ; ISSN:1521-4117. (Wiley-VCH Verlag GmbH & Co. KGaA)This study proposed an improved route towards the quant. structure detn. of large 3D nanoparticle assemblies, which required optimization of both the acquisition technique and the reconstruction algorithm. Generally, data revealed that 3D quant. results for large nanoparticle assemblies can be obtained by optimizing different aspects of the electron tomog. expt. For the acquisition, HAADF-STEM imaging is less suited and IBF-STEM imaging, cor. for the so-called cupping artifact presents the best alternative. The total variation minimization technique is presented as the most optimal approach for the 3D reconstruction. In fact through this methodol., a large (>500 nm) spherical assembly of Au nanoparticles was reconstructed while minimizing any artifacts in the reconstruction.
- 31Steinhardt, P. J.; Nelson, D. R.; Ronchetti, M. Bond-Orientational Order in Liquids and Glasses Phys. Rev. B: Condens. Matter Mater. Phys. 1983, 28, 784– 805 DOI: 10.1103/PhysRevB.28.784[Crossref], [CAS], Google Scholar31https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL3sXkslOgs7w%253D&md5=28361a8f41e7dd34826a01d7ae4e5e08Bond-orientational order in liquids and glassesSteinhardt, Paul J.; Nelson, David R.; Ronchetti, MarcoPhysical Review B: Condensed Matter and Materials Physics (1983), 28 (2), 784-805CODEN: PRBMDO; ISSN:0163-1829.Bond orientational order in mol. dynamics simulations of supercooled liqs. and in models of metallic glasses is studied. Quadratic and 3rd-order invariants formed from bond spherical harmonics allow quant. measures of cluster symmetries in these systems. A state with short-range translational order, but extended correlations in the orientations of particle clusters, starts to develop about 10% below the equil. melting temp. in a supercooled Lennard-Jones liq. The order is predominantly icosahedral, although there is also a cubic component which we attribute to the periodic boundary conditions. Results are obtained for liqs. cooled in an icosahedral pair potential as well. Only a modest amt. of orientational order appears in a relaxed Finney dense-random-packing model. In contrast, essentially perfect icosahedral bond correlations are found in alternative "amorphon" cluster models of glass structure.
- 32Wang, Y.; Teitel, S.; Dellago, C. Melting of Icosahedral Gold Nanoclusters from Molecular Dynamics Simulations J. Chem. Phys. 2005, 122, 214722 DOI: 10.1063/1.1917756[Crossref], [PubMed], [CAS], Google Scholar32https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2MXlsVeku7s%253D&md5=3948915e1b48f6c0fc0f764b1f2d3823Melting of icosahedral gold nanoclusters from molecular dynamics simulationsWang, Yanting; Teitel, S.; Dellago, ChristophJournal of Chemical Physics (2005), 122 (21), 214722/1-214722/16CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)Mol. dynamics simulations show that Au clusters with about 600-3000 atoms crystallize into a Mackay icosahedron upon cooling from the liq. A detailed surface anal. shows that the facets on the surface of the Mackay icosahedral gold clusters soften but do not premelt below the bulk melting temp. This softening is found to be due to the increasing mobility of vertex and edge atoms with temp., which leads to inter-layer and intra-layer diffusion, and a shrinkage of the av. facet size, so that the av. shape of the cluster is nearly spherical at melting.
- 33van Driel, A. F.; Allan, G.; Delerue, C.; Lodahl, P.; Vos, W. L.; Vanmaekelbergh, D. Frequency-Dependent Spontaneous Emission Rate from CdSe and CdTe Nanocrystals: Influence of Dark States Phys. Rev. Lett. 2005, 95, 236804 DOI: 10.1103/PhysRevLett.95.236804[Crossref], [PubMed], [CAS], Google Scholar33https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2MXht1Oru7nF&md5=7d8ddd3865cfbf83241a469db532e440Frequency-Dependent Spontaneous Emission Rate from CdSe and CdTe Nanocrystals: Influence of Dark Statesvan Driel, A. F.; Allan, G.; Delerue, C.; Lodahl, P.; Vos, W. L.; Vanmaekelbergh, D.Physical Review Letters (2005), 95 (23), 236804/1-236804/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)The authors studied the rate of spontaneous emission from colloidal CdSe and CdTe nanocrystals at room temp. The decay rate, obtained from luminescence decay curves, increases with the emission frequency in a supralinear way. This dependence is explained by the thermal occupation of dark exciton states at room temp., giving rise to a strong attenuation of the rate of emission. The supralinear dependence is in agreement with the results of tight-binding calcns.
- 34Verhaegh, N. A. M.; van Blaaderen, A. Dispersions of Rhodamine-Labeled Silica Spheres: Synthesis, Characterization, and Fluorescence Confocal Scanning Laser Microscopy Langmuir 1994, 10, 1427– 1438 DOI: 10.1021/la00017a019[ACS Full Text], [CAS], Google Scholar34https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2cXivVWiu7c%253D&md5=dce78e9d12343d9404e3921c65f4e280Dispersions of Rhodamine-Labeled Silica Spheres: Synthesis, Characterization, and Fluorescence Confocal Scanning Laser MicroscopyVerhaegh, Nynke A. M.; Blaaderen, Alfons vanLangmuir (1994), 10 (5), 1427-38CODEN: LANGD5; ISSN:0743-7463.Monodisperse colloidal silica spheres were synthesized with a total radius of 200 nm and labeled with the fluorescent dye rhodamine isothiocyanate (RITC) in a core of 100 nm radius. The particles were characterized by TEM and by static and dynamic light scattering. The fluorescence properties and dye concns. in the particles were measured with fluorescence and absorption spectroscopy. Stable dispersions of these hydrophilic, charge-stabilized silica spheres in polar solvents and of organophilic, sterically stabilized, 1-octadecanol-coated silica spheres in apolar solvents were studied with fluorescence confocal scanning laser microscopy (CSLM). The bleachability of these particles was detd. with CSLM and compared with particles labeled with the dye fluorescein isothiocyanate (FITC). The possibilities and limitations of confocal microscopy to study individual fluorescent particles in the bulk of concd. model dispersions are discussed and demonstrated with CSLM graphs of a time series showing colloidal crystn. (crystal growth rate ∼ 4 μm/s), an equil. between a colloidal liq. and colloidal crystal interface, and a binary mixt. of RITC- and FITC-labeled spheres. Further, the feasibility of by using the RITC-labeled spheres with other techniques relying on fluorescence is also discussed.
- 35Li, J. J.; Wang, Y. A.; Guo, W.; Keay, J. C.; Mishima, T. D.; Johnson, M. B.; Peng, X. Large-Scale Synthesis of Nearly Monodisperse CdSe/CdS Core/Shell Nanocrystals Using Air-Stable Reagents via Successive Ion Layer Adsorption and Reaction J. Am. Chem. Soc. 2003, 125, 12567– 12575 DOI: 10.1021/ja0363563[ACS Full Text], [CAS], Google Scholar35https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3sXnsVOisLs%253D&md5=8d5e57d2c474afe888f40b37069364deLarge-Scale Synthesis of Nearly Monodisperse CdSe/CdS Core/Shell Nanocrystals Using Air-Stable Reagents via Successive Ion Layer Adsorption and ReactionLi, J. Jack; Wang, Y. Andrew; Guo, Wenzhuo; Keay, Joel C.; Mishima, Tetsuya D.; Johnson, Matthew B.; Peng, XiaogangJournal of the American Chemical Society (2003), 125 (41), 12567-12575CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Successive ion layer adsorption and reaction (SILAR) originally developed for the deposition of thin films on solid substrates from soln. baths is introduced as a technique for the growth of high-quality core/shell nanocrystals of compd. semiconductors. The growth of the shell was designed to grow 1 monolayer at a time by alternating injections of air-stable and inexpensive cationic and anionic precursors into the reaction mixt. with core nanocrystals. The principles of SILAR were demonstrated by the CdSe/CdS core/shell model system using its shell-thickness-dependent optical spectra as the probes with CdO and elemental S as the precursors. For this reaction system, a relatively high temp., ∼220-240°, is essential for SILAR to fully occur. The synthesis can be readily performed on a multigram scale. The size distribution of the core/shell nanocrystals was maintained even after 5 monolayers of CdS shell (equiv. to ∼10 times vol. increase for a 3.5 nm CdSe nanocrystal) were grown onto the core nanocrystals. The epitaxial growth of the core/shell structures was verified by optical spectroscopy, TEM, XRD, and XPS. The luminescence quantum yield (PL QY) of the as-prepd. CdSe/CdS core/shell nanocrystals ranged from 20% to 40%, and the PL full-width at half-max. (fwhm) was maintained between 23 and 26 nm, even for those nanocrystals for which the UV-visible and PL peaks red shifted by ∼50 nm from that of the core nanocrystals. Several types of brightening phenomena were obsd., some of which can further boost the PL QY of the core/shell nanocrystals. The CdSe/CdS core/shell nanocrystals are superior in comparison to the highly luminescent CdSe plain core nanocrystals. The SILAR technique reported here can also be used for the growth of complex colloidal semiconductor nanostructures, such as quantum shells and colloidal quantum wells.
- 36Bae, W. K.; Kwak, J.; Park, J. W.; Char, K.; Lee, C.; Lee, S. Highly Efficient Green-Light-Emitting Diodes Based on [email protected] Quantum Dots with a Chemical-Composition Gradient Adv. Mater. 2009, 21, 1690– 1694 DOI: 10.1002/adma.200801908[Crossref], [CAS], Google Scholar36https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXltFGhsr0%253D&md5=8b102d3383d4cab287124d60c8bc0e61Highly Efficient Green-Light-Emitting Diodes Based on [email protected] Quantum Dots with a Chemical-Composition GradientBae, Wan Ki; Kwak, Jeonghun; Park, Ji Won; Char, Kookheon; Lee, Changhee; Lee, SeonghoonAdvanced Materials (Weinheim, Germany) (2009), 21 (17), 1690-1694CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)The Green-emitting LEDs based of quantum dots were fabricated and their properties studied. The spectral properties of prepd. films were obtained and EL and current efficiency for diodes were discussed.
- 37Lee, K.; Lee, J.; Song, W.; Ko, H.; Lee, C.; Lee, J.; Yang, H. Higly Efficient, Color-Pure, Color-Stable Blue Quantum Dot Light-Emitting Devices ACS Nano 2013, 7, 7295– 7302 DOI: 10.1021/nn402870e
- 38van Aarle, W.; Palenstijn, W. J.; De Beenhouwer, J.; Altantzis, T.; Bals, S.; Batenburg, K. J.; Sijbers, J. The ASTRA Toolbox: A Platform for Advanced Algorithm Development in Electron Tomography Ultramicroscopy 2015, 157, 35– 47 DOI: 10.1016/j.ultramic.2015.05.002[Crossref], [PubMed], [CAS], Google Scholar38https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXotVKhsLs%253D&md5=3712da2f93e931cb64ef3c7e65dee01eThe ASTRA Toolbox: A platform for advanced algorithm development in electron tomographyvan Aarle, Wim; Palenstijn, Willem Jan; De Beenhouwer, Jan; Altantzis, Thomas; Bals, Sara; Batenburg, K. Joost; Sijbers, JanUltramicroscopy (2015), 157 (), 35-47CODEN: ULTRD6; ISSN:0304-3991. (Elsevier B.V.)We present the ASTRA Toolbox as an open platform for 3D image reconstruction in tomog. Most of the software tools that are currently used in electron tomog. offer limited flexibility with respect to the geometrical parameters of the acquisition model and the algorithms used for reconstruction. The ASTRA Toolbox provides an extensive set of fast and flexible building blocks that can be used to develop advanced reconstruction algorithms, effectively removing these limitations. We demonstrate this flexibility, the resulting reconstruction quality, and the computational efficiency of this toolbox by a series of expts., based on exptl. dual-axis tilt series.
- 39van Aarle, W.; Palenstijn, W. J.; Cant, J.; Janssens, E.; Bleichrodt, F.; Dabravolski, A.; Beenhouwer, J. De; Batenburg, K. J.; Sijbers, J. Fast and Flexible X-Ray Tomography Using the ASTRA Toolbox Opt. Express 2016, 24, 25129– 25147 DOI: 10.1364/OE.24.025129[Crossref], [PubMed], [CAS], Google Scholar39https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC2snksFaqtA%253D%253D&md5=5bebcfefa69d3bc59e8184d9adf1e0ffFast and flexible X-ray tomography using the ASTRA toolboxvan Aarle Wim; Palenstijn Willem Jan; Cant Jeroen; Janssens Eline; Bleichrodt Folkert; Dabravolski Andrei; De Beenhouwer Jan; Joost Batenburg K; Sijbers JanOptics express (2016), 24 (22), 25129-25147 ISSN:.Object reconstruction from a series of projection images, such as in computed tomography (CT), is a popular tool in many different application fields. Existing commercial software typically provides sufficiently accurate and convenient-to-use reconstruction tools to the end-user. However, in applications where a non-standard acquisition protocol is used, or where advanced reconstruction methods are required, the standard software tools often are incapable of computing accurate reconstruction images. This article introduces the ASTRA Toolbox. Aimed at researchers across multiple tomographic application fields, the ASTRA Toolbox provides a highly efficient and highly flexible open source set of tools for tomographic projection and reconstruction. The main features of the ASTRA Toolbox are discussed and several use cases are presented.
- 40Palenstijn, W. J.; Batenburg, K. J.; Sijbers, J. Performance Improvements for Iterative Electron Tomography Reconstruction Using Graphics Processing Units (GPUs) J. Struct. Biol. 2011, 176, 250– 253 DOI: 10.1016/j.jsb.2011.07.017[Crossref], [PubMed], [CAS], Google Scholar40https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC3Mfnslygsw%253D%253D&md5=7799f40ff4990fbf11f37f13d421aa74Performance improvements for iterative electron tomography reconstruction using graphics processing units (GPUs)Palenstijn W J; Batenburg K J; Sijbers JJournal of structural biology (2011), 176 (2), 250-3 ISSN:.Iterative reconstruction algorithms are becoming increasingly important in electron tomography of biological samples. These algorithms, however, impose major computational demands. Parallelization must be employed to maintain acceptable running times. Graphics Processing Units (GPUs) have been demonstrated to be highly cost-effective for carrying out these computations with a high degree of parallelism. In a recent paper by Xu et al. (2010), a GPU implementation strategy was presented that obtains a speedup of an order of magnitude over a previously proposed GPU-based electron tomography implementation. In this technical note, we demonstrate that by making alternative design decisions in the GPU implementation, an additional speedup can be obtained, again of an order of magnitude. By carefully considering memory access locality when dividing the workload among blocks of threads, the GPU's cache is used more efficiently, making more effective use of the available memory bandwidth.
- 41Schlossmacher, P.; Klenov, D. O.; Freitag, B.; von Harrach, H. S. Enhanced Detection Sensitivity with a New Windowless XEDS System for AEM Based on Silicon Drift Detector Technology Microsc. Today 2010, 18, 14– 20 DOI: 10.1017/S1551929510000404[Crossref], [CAS], Google Scholar41https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXhtVajsrfF&md5=e80c6540f5bbcd30846eb8d3cbd1389aEnhanced detection sensitivity with a new windowless XEDS system for AEM based on silicon drift detector technologySchlossmacher, P.; Klenov, D. O.; Freitag, B.; von Harrach, H. S.Microscopy Today (2010), 18 (4), 14, 16, 18-20CODEN: MITOFQ; ISSN:1551-9295. (Cambridge University Press)A new X-ray energy dispersive spectrometer (XEDS) system is described and application examples from a new anal. electron microscope (AEM) system are presented. The novel ChemiSTEM technol. on the Tecnai Osiris comprises this new proprietary XEDS detector system (Super-X design) in combination with a high- brightness Schottky field emission electron source (X-FEG) as the two major components. In addn. to the Schottky FEG source, the new detector system shows greatly enhanced detection sensitivity due to four detectors integrated deeply into the objective lens, windowless silicon drift detector technol. with shutters, and high-speed electronics readout. This new system architecture provides many performance benefits, such as improved light element detection, better sample tilt response, faster mapping, and esp. enhanced system detection sensitivity.
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Abstract
Figure 1
Figure 1. TEM images and optical properties of the original QDs. (a–c) Representative transmission electron micrographs (scale bar 50 nm) of (a) the red emitting QDs (diameter: 10.3 ± 1.0 nm), (b) the green emitting QDs (diameter: 11.0 ± 1.1 nm), and (c) the blue emitting QDs (diameter: 10.5 ± 1.3 nm). Insets are models of the QDs. (d–f) Absorption (dashed lines) and emission (solid lines) spectra of three different populations of QDs used for the self-assembly.
Figure 2
Figure 2. Structural characterization of the SPs. (a) SE-STEM image of two SPs (scale bar 200 nm). The inset shows a magnification of one of the particles (scale bar 20 nm). Individual QDs can be clearly distinguished. (b, c) 2D HAADF-STEM images (scale bars 50 nm) of a small SP for which electron tomography has been performed (b), and a 3D visualization of the 3D tomographic reconstruction of the same SP (c). (d) Slice through the center of the 3D reconstruction of the SP (scale bar 50 nm). Individual QDs can be clearly recognized as well as their relative position, showing the irregular inner structure. (e) Fast Fourier transform of the slice of panel d (scale bar 0.1 nm–1).
Figure 3
Figure 3. Optical characterization of the SPs. (a) Confocal microscopy image of a set of SPs drop-casted and dried on a glass slide and excited with UV excitation (scale bar 3 μm). (b) Confocal fluorescence image of different SPs (scale bar 1 μm). The blue-green emission (450–550 nm) is shown in green, while the red emission (600–700 nm) is shown in red; the image is deconvolved through the modeling of the point spread function of the microscope. The inset shows the signal collected along the white line drawn in the figure coming from the two detectors. (c–e) Emission spectra of some of the SPs presented in panel a, indicated with the green, red, or blue frame.
Figure 4
Figure 4. Optical properties of SPs compared to suspensions of the constituent QDs. (a) Emission spectrum of an ensemble of white light-emitting SPs (black) and of the three separate dispersions of the constituent QDs (colored; each scaled to match the maximum intensity of the corresponding peak in the composite spectrum). (b) PL decay traces of red QDs freely dispersed in toluene (red closed circles), assembled in water-dispersed SPs of red QDs (red open circles), and assembled in a white light-emitting SPs (gray open circles). The red line is a fit to the PL decay of red SPs, and the black line to the decay of white-light emitting SPs (see Supporting Information for an explanation of the fitting procedure). Same for (c) green QDs and (d) blue QDs.
Figure 5
Figure 5. CIE chromaticity diagram of the QDs and the SPs. Left: CIE diagram representing different SP batches as obtained by changing the ratio between the three QDs populations. The vertices of the triangle represent the coordinates of the three types of QDs. Therefore, the area of the triangle represents all the possible colors SPs can have. Right (1–3): Digital true-color photographs of the QDs dispersed in solution when illuminated with a UV laser. (4) Digital photograph of a dispersion of the SPs, composed of the three types of QDs, emitting white light.
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- 3Chen, O.; Zhao, J.; Chauhan, V. P.; Cui, J.; Wong, C.; Harris, D. K.; Wei, H.; Han, H.-S.; Fukumura, D.; Jain, R. K.; Bawendi, M. G. Compact High-Quality CdSe-CdS Core-Shell Nanocrystals with Narrow Emission Linewidths and Suppressed Blinking Nat. Mater. 2013, 12, 445– 451 DOI: 10.1038/nmat3539[Crossref], [PubMed], [CAS], Google Scholar3https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhvFSmsr0%253D&md5=838b3a049dcde2917c57c9bb6ac5cd66Compact high-quality CdSe-CdS core-shell nanocrystals with narrow emission linewidths and suppressed blinkingChen, Ou; Zhao, Jing; Chauhan, Vikash P.; Cui, Jian; Wong, Cliff; Harris, Daniel K.; Wei, He; Han, Hee-Sun; Fukumura, Dai; Jain, Rakesh K.; Bawendi, Moungi G.Nature Materials (2013), 12 (5), 445-451CODEN: NMAACR; ISSN:1476-1122. (Nature Publishing Group)High particle uniformity, high luminescence quantum yields, narrow and sym. emission spectral lineshapes and min. single-dot emission intermittency (known as blinking) were recognized as universal requirements for the successful use of colloidal quantum dots in nearly all optical applications. Synthesizing samples that simultaneously meet all these 4 criteria proved challenging. The synthesis of such high-quality CdSe-CdS core-shell quantum dots in an optimized process that maintains a slow growth rate of the shell through the use of octanethiol and Cd oleate as precursors is reported. In contrast with previous observations, single-dot blinking is significantly suppressed with only a relatively thin shell. The elimination of the ensemble luminescence photodarkening that is an intrinsic consequence of quantum dot blinking statistical ageing is demonstrated. The small size and high luminescence quantum yields of these novel quantum dots render them superior in vivo imaging agents compared with conventional quantum dots. It is anticipated that these quantum dots will result in significant improvement in the performance of quantum dots in other applications such as solid-state lighting and illumination.
- 4Christodoulou, S.; Vaccaro, G.; Pinchetti, V.; De Donato, F.; Grim, J. Q.; Casu, a.; Genovese, a.; Vicidomini, G.; Diaspro, a.; Brovelli, S.; Manna, L.; Moreels, I. Synthesis of Highly Luminescent Wurtzite CdSe/CdS Giant-Shell Nanocrystals Using a Fast Continuous Injection Route J. Mater. Chem. C 2014, 2, 3439 DOI: 10.1039/c4tc00280f[Crossref], [CAS], Google Scholar4https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXlsFyrurY%253D&md5=dbc871782c730e500e58f0178f98ebedSynthesis of highly luminescent wurtzite CdSe/CdS giant-shell nanocrystals using a fast continuous injection routeChristodoulou, S.; Vaccaro, G.; Pinchetti, V.; De Donato, F.; Grim, J. Q.; Casu, A.; Genovese, A.; Vicidomini, G.; Diaspro, A.; Brovelli, S.; Manna, L.; Moreels, I.Journal of Materials Chemistry C: Materials for Optical and Electronic Devices (2014), 2 (17), 3439-3447CODEN: JMCCCX; ISSN:2050-7534. (Royal Society of Chemistry)We synthesized CdSe/CdS giant-shell nanocrystals, with a CdSe core diam. between 2.8 nm and 5.5 nm, and a CdS shell thickness of up to 7-8 nm (equiv. to about 20 monolayers of CdS). Both the core and shell have a wurtzite crystal structure, yielding epitaxial growth of the shell and nearly defect-free crystals. As a result, the photoluminescence (PL) quantum efficiency (QE) is as high as 90%. Quant. PL measurements at various excitation wavelengths allow us to sep. the nonradiative decay into contributions from interface and surface trapping, giving us pathways for future optimization of the structure. In addn., the NCs do not blink, and the giant shell and concurring strong electron delocalization efficiently suppress Auger recombination, yielding a biexciton lifetime of about 15 ns. The corresponding biexciton PL QE equals 11% in 5.5/18.1 nm CdSe/CdS. Variable-temp. time-resolved PL and PL under magnetic fields further reveal that the emission at cryogenic temp. originates from a neg. trion-state, in agreement with other CdSe/CdS giant-shell systems reported in the literature.
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- 6García-Santamaría, F.; Chen, Y.; Vela, J.; Schaller, R. D.; Hollingsworth, J. a; Klimov, V. Suppressed Auger Recombination in “Giant” Nanocrystals Boosts Optical Gain Performance Nano Lett. 2009, 9, 3482– 3488 DOI: 10.1021/nl901681d[ACS Full Text], [CAS], Google Scholar6https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXmvV2ktLg%253D&md5=b5f611debf8ea310425d554049de1950Suppressed Auger Recombination in "Giant" Nanocrystals Boosts Optical Gain PerformanceGarcia-Santamaria, Florencio; Chen, Yongfen; Vela, Javier; Schaller, Richard D.; Hollingsworth, Jennifer A.; Klimov, Victor I.Nano Letters (2009), 9 (10), 3482-3488CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)Many potential applications of semiconductor nanocrystals are hindered by nonradiative Auger recombination wherein the electron-hole (exciton) recombination energy is transferred to a 3rd charge carrier. This process severely limits the lifetime and bandwidth of optical gain, leads to large nonradiative losses in light-emitting diodes and photovoltaic cells, and is believed to be responsible for intermittency (blinking) of emission from single nanocrystals. The development of nanostructures in which Auger recombination is suppressed has recently been the subject of much research in the colloidal nanocrystal field. Here, the authors provide direct exptl. evidence that so-called giant nanocrystals consisting of a small CdSe core and a thick CdS shell exhibit a significant (orders of magnitude) suppression of Auger decay rates. As a consequence, even multiexcitons of a very high order exhibit significant emission efficiencies, which allows the authors to demonstrate optical amplification with an extraordinarily large bandwidth (>500 meV) and record low excitation thresholds. This demonstration represents an important milestone toward practical lasing technologies using soln.-processable colloidal nanoparticles.
- 7Mahler, B.; Spinicelli, P.; Buil, S.; Quelin, X.; Hermier, J.-P.; Dubertret, B. Towards Non-Blinking Colloidal Quantum Dots Nat. Mater. 2008, 7, 659– 664 DOI: 10.1038/nmat2222[Crossref], [PubMed], [CAS], Google Scholar7https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXovFWrt7c%253D&md5=51fcba04adc6f1aaecb939dd1cbbd8e7Towards non-blinking colloidal quantum dotsMahler, Benoit; Spinicelli, Piernicola; Buil, Stephanie; Quelin, Xavier; Hermier, Jean-Pierre; Dubertret, BenoitNature Materials (2008), 7 (8), 659-664CODEN: NMAACR; ISSN:1476-1122. (Nature Publishing Group)At a single-mol. level, fluorophore emission intensity fluctuates between bright and dark states. These fluctuations, known as blinking, limit the use of fluorophores in single-mol. expts. The dark-state duration shows a universal heavy-tailed power-law distribution characterized by the occurrence of long nonemissive periods. Novel CdSe-CdS core-shell quantum dots were synthesized with thick cryst. shells, 68% of which do not blink when obsd. individually at 33 Hz for 5 min. A direct correlation was established between shell thickness and blinking occurrences. The statistics of dark periods that appear at high acquisition rates (1 kHz) are not heavy tailed, in striking contrast with previous observations. Blinking statistics are thus not as universal as thought so far. It is anticipated that the results will help to better understand the physicochem. of single-fluorophore emission and rationalize the design of other fluorophores that do not blink.
- 8Hollingsworth, J. A. Heterostructuring Nanocrystal Quantum Dots toward Intentional Suppression of Blinking and Auger Recombination Chem. Mater. 2013, 25, 1318– 1331 DOI: 10.1021/cm304161d[ACS Full Text], [CAS], Google Scholar8https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXjsFaru74%253D&md5=995b022a3909f6950136590b5e6f7f5bHeterostructuring Nanocrystal Quantum Dots Toward Intentional Suppression of Blinking and Auger RecombinationHollingsworth, Jennifer A.Chemistry of Materials (2013), 25 (8), 1318-1331CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)A review. At the level of a single particle, nanocrystal quantum dots (NQDs) fluoresce intermittently or blink. They are also characterized by an efficient nonradiative recombination process known as Auger recombination (AR). Recently, new approaches to NQD heterostructuring were developed that directly impact both blinking and AR, resulting in dramatic suppression of these unwanted processes. The 3 successful hetero-NQD motifs are reviewed here: (1) interfacial alloying, (2) thick or giant shells, and (3) specific type-II electronic structures. These approaches, which rely on modifying or tuning internal NQD core/shell structures, are compared with alternative strategies for blinking suppression that rely, instead, on surface modifications or surface-mediated interactions. Finally, in each case, the unique synthetic approaches or challenges addressed that have driven the realization of novel and important functionality are discussed, along with the implications for development of a comprehensive materials design strategy for blinking and AR-suppressed heterostructured NQDs.
- 9Park, Y.-S.; Bae, W. K.; Baker, T.; Lim, J.; Klimov, V. I. Effect of Auger Recombination on Lasing in Heterostructured Quantum Dots with Engineered Core/Shell Interfaces Nano Lett. 2015, 15, 7319– 7328 DOI: 10.1021/acs.nanolett.5b02595[ACS Full Text], [CAS], Google Scholar9https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhsFCjurjF&md5=3132d3f8924b469db45cf84639d33401Effect of Auger Recombination on Lasing in Heterostructured Quantum Dots with Engineered Core/Shell InterfacesPark, Young-Shin; Bae, Wan Ki; Baker, Thomas; Lim, Jaehoon; Klimov, Victor I.Nano Letters (2015), 15 (11), 7319-7328CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)Nanocrystal quantum dots (QDs) are attractive materials for applications as laser media because of their bright, size-tunable emission and the flexibility afforded by colloidal synthesis. Nonradiative Auger recombination hampers optical amplification in QDs by rapidly depleting the population of gain-active multiexciton states. To elucidate the role of Auger recombination in QD lasing and isolate its influence from other factors that might affect optical gain, 2 types of CdSe/CdS core/shell QDs with the same core radii and the same total sizes but different properties of the core/shell interface (sharp vs. smooth) were studied. These samples exhibit distinctly different biexciton Auger lifetimes but are otherwise virtually identical. The suppression of Auger recombination in the sample with a smooth (alloyed) interface results in a notable improvement in the optical gain performance manifested in the redn. of the threshold for amplified spontaneous emission and the ability to produce dual-color lasing involving both the band-edge (1S) and the higher-energy (1P) electronic states. The authors develop a model, which explicitly accounts for the multiexciton nature of optical gain in QDs, and use it to analyze the competition between stimulated emission from multiexcitons and their decay via Auger recombination. These studies reemphasize the importance of Auger recombination control for the realization of real-life QD-based lasing technols. and offer practical strategies for suppression of Auger recombination via interface engineering in core/shell structures.
- 10Klimov, V. I.; Mikhailovsky, a. a.; Xu, S.; Malko, a; Hollingsworth, J. a.; Leatherdale, C. a; Eisler, H.-J.; Bawendi, M. G. Optical Gain and Stimulated Emission in Nanocrystal Quantum Dots Science (Washington, DC, U. S.) 2000, 290, 314– 317 DOI: 10.1126/science.290.5490.314[Crossref], [PubMed], [CAS], Google Scholar10https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3cXnsVGisL0%253D&md5=9cf79ab10ed1fb0ce212182066c89b62Optical gain and stimulated emission in nanocrystal quantum dotsKlimov, V. I.; Mikhailovsky, A. A.; Xu, Su; Malko, A.; Hollingsworth, J. A.; Leatherdale, C. A.; Eisler, H.-J.; Bawendiz, M. G.Science (Washington, D. C.) (2000), 290 (5490), 314-317CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)The development of optical gain in chem. synthesized semiconductor nanoparticles (nanocrystal quantum dots) has been intensely studied as the first step toward nanocrystal quantum dot lasers. The authors examd. the competing dynamical processes involved in optical amplification and lasing in nanocrystal quantum dots and found that, despite a highly efficient intrinsic nonradiative Auger recombination, large optical gain can be developed at the wavelength of the emitting transition for close-packed solids of these dots. Narrow-band stimulated emission with a pronounced gain threshold at wavelengths tunable with the size of the nanocrystal was obsd., as expected from quantum confinement effects. These results unambiguously demonstrate the feasibility of nanocrystal quantum dot lasers.
- 11Klimov, V. Spectral and Dynamical Properties of Multiexcitons in Semiconductor Nanocrystals Annu. Rev. Phys. Chem. 2007, 58, 635– 673 DOI: 10.1146/annurev.physchem.58.032806.104537[Crossref], [PubMed], [CAS], Google Scholar11https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXlslSitL4%253D&md5=255b3af2784714c438097359fb36d2b6Spectral and dynamical properties of multiexcitons in semiconductor nanocrystalsKlimov, Victor I.Annual Review of Physical Chemistry (2007), 58 (), 635-673CODEN: ARPLAP; ISSN:0066-426X. (Annual Reviews Inc.)A review. Because of the strong spatial confinement of electronic wave functions and reduced dielec. screening, the effects of carrier-carrier Coulomb interactions are greatly enhanced in semiconductor nanocrystals (NCs) compared with those in bulk materials. These interactions open a highly efficient decay channel via Auger recombination, which represents a dominant recombination pathway for multiexcitons in NCs. Also, strong Coulomb coupling between charge carriers leads to extremely efficient direct photogeneration of multiexcitons by single photons via carrier (or exciton) multiplication. This review focuses on spectral and dynamical properties of multiexcitons in semiconductor NCs. The specific topics discussed here include the structure of NC electronic states, spectral signatures of multiexcitons in transient absorption and photoluminescence, exciton-exciton interaction energies, Auger recombination, and carrier multiplication. This chapter also briefly reviews the implications of multiexciton effects for practical technologies, such as NC lasing and photovoltaics.
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- 13Bruchez, M., Jr.; Moronne, M.; Gin, P.; Weiss, S.; Alivisatos, A. P. Semiconductor Nanocrystals as Fluorescent Biological Labels Science 1998, 281, 2013– 2016 DOI: 10.1126/science.281.5385.2013[Crossref], [PubMed], [CAS], Google Scholar13https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1cXmtlKgurw%253D&md5=db36fdbbfbc2facf264c3f98c1c8efcbSemiconductor nanocrystals as fluorescent biological labelsBruchez, Marcel, Jr.; Moronne, Mario; Gin, Peter; Weiss, Shimon; Alivisatos, A. PaulScience (Washington, D. C.) (1998), 281 (5385), 2013-2016CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)Semiconductor nanocrystals were prepd. for use as fluorescent probes in biol. staining and diagnostics. Compared with conventional fluorophores, the nanocrystals have a narrow, tunable, sym. emission spectrum and are photochem. stable. The advantages of the broad, continuous excitation spectrum were demonstrated in a dual-emission, single-excitation labeling expt. on mouse fibroblasts. These nanocrystal probes are thus complementary and in some cases may be superior to existing fluorophores.
- 14Michalet, X.; Pinaud, F.; Bentolila, L.; Tsay, J.; Doose, S.; Li, J.; Sundaresan, G.; Wu, A.; Gambhir, S.; Weiss, S. Quantum Dots for Live Cells, in Vivo Imaging, and Diagnostics Science (Washington, DC, U. S.) 2005, 307, 538– 544 DOI: 10.1126/science.1104274[Crossref], [PubMed], [CAS], Google Scholar14https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2MXmslOhtw%253D%253D&md5=03a28864cfd8c3c4269cc9919d1eafb9Quantum Dots for Live Cells, in Vivo Imaging, and DiagnosticsMichalet, X.; Pinaud, F. F.; Bentolila, L. A.; Tsay, J. M.; Doose, S.; Li, J. J.; Sundaresan, G.; Wu, A. M.; Gambhir, S. S.; Weiss, S.Science (Washington, DC, United States) (2005), 307 (5709), 538-544CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)A review. Research on fluorescent semiconductor nanocrystals (also known as quantum dots or qdots) has evolved over the past two decades from electronic materials science to biol. applications. We review current approaches to the synthesis, solubilization, and functionalization of qdots and their applications to cell and animal biol. Recent examples of their exptl. use include the observation of diffusion of individual glycine receptors in living neurons and the identification of lymph nodes in live animals by near-IR emission during surgery. The new generations of qdots have far-reaching potential for the study of intracellular processes at the single-mol. level, high-resoln. cellular imaging, long-term in vivo observation of cell trafficking, tumor targeting, and diagnostics.
- 15Meinardi, F.; McDaniel, H.; Carulli, F.; Colombo, A.; Velizhanin, K. a.; Makarov, N. S.; Simonutti, R.; Klimov, V. I.; Brovelli, S. Highly Efficient Large-Area Colourless Luminescent Solar Concentrators Using Heavy-Metal-Free Colloidal Quantum Dots Nat. Nanotechnol. 2015, 10, 878– 885 DOI: 10.1038/nnano.2015.178[Crossref], [PubMed], [CAS], Google Scholar15https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhtlyls7vO&md5=b63662c4e01349d552589031b5cc71deHighly efficient large-area colorless luminescent solar concentrators using heavy-metal-free colloidal quantum dotsMeinardi, Francesco; McDaniel, Hunter; Carulli, Francesco; Colombo, Annalisa; Velizhanin, Kirill A.; Makarov, Nikolay S.; Simonutti, Roberto; Klimov, Victor I.; Brovelli, SergioNature Nanotechnology (2015), 10 (10), 878-885CODEN: NNAABX; ISSN:1748-3387. (Nature Publishing Group)Luminescent solar concentrators serving as semitransparent photovoltaic windows could become an important element in net zero energy consumption buildings of the future. Colloidal quantum dots are promising materials for luminescent solar concentrators as they can be engineered to provide the large Stokes shift necessary for suppressing reabsorption losses in large-area devices. Existing Stokes-shift-engineered quantum dots allow for only partial coverage of the solar spectrum, which limits their light-harvesting ability and leads to coloring of the luminescent solar concentrators, complicating their use in architecture. Here, we use quantum dots of ternary I-III-VI2 semiconductors to realize the first large-area quantum dot-luminescent solar concentrators free of toxic elements, with reduced reabsorption and extended coverage of the solar spectrum. By incorporating CuInSexS2-x quantum dots into photo-polymd. poly(lauryl methacrylate), we obtain freestanding, colorless slabs that introduce no distortion to perceived colors and are thus well suited for the realization of photovoltaic windows. Thanks to the suppressed reabsorption and high emission efficiencies of the quantum dots, we achieve an optical power efficiency of 3.2%. Ultrafast spectroscopy studies suggest that the Stokes-shifted emission involves a conduction-band electron and a hole residing in an intragap state assocd. with a native defect.
- 16Meinardi, F.; Colombo, A.; Velizhanin, K. a.; Simonutti, R.; Lorenzon, M.; Beverina, L.; Viswanatha, R.; Klimov, V.; Brovelli, S. Large-Area Luminescent Solar Concentrators Based on “Stokes-Shift-Engineered” Nanocrystals in a Mass-Polymerized PMMA Matrix Nat. Photonics 2014, 8, 392– 399 DOI: 10.1038/nphoton.2014.54[Crossref], [CAS], Google Scholar16https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXmtlWqsbg%253D&md5=cfa9667bf689b3f506ee0c26368f98efLarge-area luminescent solar concentrators based on 'Stokes-shift-engineered' nanocrystals in a mass-polymerized PMMA matrixMeinardi, Francesco; Colombo, Annalisa; Velizhanin, Kirill A.; Simonutti, Roberto; Lorenzon, Monica; Beverina, Luca; Viswanatha, Ranjani; Klimov, Victor I.; Brovelli, SergioNature Photonics (2014), 8 (5), 392-399CODEN: NPAHBY; ISSN:1749-4885. (Nature Publishing Group)Luminescent solar concentrators are cost-effective complements to semiconductor photovoltaics that can boost the output of solar cells and allow for the integration of photovoltaic-active architectural elements into buildings (for example, photovoltaic windows). Colloidal quantum dots are attractive for use in luminescent solar concentrators, but their small Stokes shift results in reabsorption losses that hinder the realization of large-area devices. Here, we use 'Stokes-shift-engineered' CdSe/CdS quantum dots with giant shells (giant quantum dots) to realize luminescent solar concentrators without reabsorption losses for device dimensions up to tens of centimeters. Monte-Carlo simulations show a 100-fold increase in efficiency using giant quantum dots compared with core-only nanocrystals. We demonstrate the feasibility of this approach by using high-optical-quality quantum dot-polymethylmethacrylate nanocomposites fabricated using a modified industrial method that preserves the light-emitting properties of giant quantum dots upon incorporation into the polymer. Study of these luminescent solar concentrators yields optical efficiencies >10% and an effective concn. factor of 4.4. These results demonstrate the significant promise of Stokes-shift-engineered quantum dots for large-area luminescent solar concentrators.
- 17Bradshaw, L. R.; Knowles, K. E.; McDowall, S.; Gamelin, D. R. Nanocrystals for Luminescent Solar Concentrators Nano Lett. 2015, 15, 1315– 1323 DOI: 10.1021/nl504510t[ACS Full Text], [CAS], Google Scholar17https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXmvFSntA%253D%253D&md5=66c24439a8954a8aa26bff77aca40fe7Nanocrystals for Luminescent Solar ConcentratorsBradshaw, Liam R.; Knowles, Kathryn E.; McDowall, Stephen; Gamelin, Daniel R.Nano Letters (2015), 15 (2), 1315-1323CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)Luminescent solar concentrators (LSCs) harvest sunlight over large areas and conc. this energy onto photovoltaics or for other uses by transporting photons through macroscopic waveguides. Although attractive for lowering solar energy costs, LSCs remain severely limited by luminophore reabsorption losses. Here, the authors report a quant. comparison of 4 types of nanocrystal (NC) phosphors recently proposed to minimize reabsorption in large-scale LSCs: 2 nanocrystal heterostructures and 2 doped nanocrystals. Exptl. and numerical analyses both show that even the small core absorption of the leading NC heterostructures causes major reabsorption losses at relatively short transport lengths. Doped NCs outperform the heterostructures substantially in this crit. property. A new LSC phosphor is introduced, nanocryst. Cd1-xCuxSe, that outperforms all other leading NCs by a significant margin in both small- and large-scale LSCs under full-spectrum conditions.
- 18Shirasaki, Y.; Supran, G. J.; Bawendi, M. G.; Bulović, V. Emergence of Colloidal Quantum-Dot Light-Emitting Technologies Nat. Photonics 2013, 7, 13– 23 DOI: 10.1038/nphoton.2012.328[Crossref], [CAS], Google Scholar18https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XhvV2ntLfI&md5=9ce4673b68f86faa7c83212c053193c4Emergence of colloidal quantum-dot light-emitting technologiesShirasaki, Yasuhiro; Supran, Geoffrey J.; Bawendi, Moungi G.; Bulovic, VladimirNature Photonics (2013), 7 (1), 13-23CODEN: NPAHBY; ISSN:1749-4885. (Nature Publishing Group)A review. Since their inception 18 years ago, elec. driven colloidal quantum-dot light-emitting devices (QD-LEDs) have increased in external quantum efficiency from less than 0.01% to around 18%. The high luminescence efficiency and uniquely size-tunable color of soln.-processable semiconducting colloidal QDs highlight the potential of QD-LEDs for use in energy-efficient, high-color-quality thin-film display and solid-state lighting applications. Indeed, last year saw the first demonstrations of elec. driven full-color QD-LED displays, which foreshadow QD technologies that will transcend the optically excited QD-enhanced lighting products already available today. We here discuss the key advantages of using QDs as luminophores in LEDs and outline the operating mechanisms of four types of QD-LED. State-of-the-art visible-wavelength LEDs and the promise of near-IR and heavy-metal-free devices are also highlighted. As QD-LED efficiencies approach those of mol. org. LEDs, we identify the key scientific and technol. challenges facing QD-LED commercialization and offer our outlook for on-going strategies to overcome these challenges.
- 19Kim, J.-H.; Jo, D.-Y.; Lee, K.-H.; Jang, E.-P.; Han, C.-Y.; Jo, J.-H.; Yang, H. White Electroluminescent Lighting Device Based on a Single Quantum Dot Emitter Adv. Mater. 2016, 28, 5093– 5098 DOI: 10.1002/adma.201600815[Crossref], [PubMed], [CAS], Google Scholar19https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XntFCgtbg%253D&md5=c25062f2d1998f2b0e0d12c98c13ece5White Electroluminescent Lighting Device Based on a Single Quantum Dot EmitterKim, Jong-Hoon; Jo, Dae-Yeon; Lee, Ki-Heon; Jang, Eun-Pyo; Han, Chang-Yeol; Jo, Jung-Ho; Yang, HeesunAdvanced Materials (Weinheim, Germany) (2016), 28 (25), 5093-5098CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)Cu/Ga ratio-varied Cu-Ga-S (CGS)/ZnS quantum dots (QDs) were synthesized, finding that Cu deficiency played crit. roles in controlling their absorption and luminescence (PL) properties and that the nominal ratio of Cu/Ga = 1/8 was the most suitable in securing the widest visible coverage toward white emission as well as high QY. The highest QY ≤76% was achievable by further adjusting the ZnS-shelling period of Cu/Ga = 1.8 based QDs. Using the resulting QDs, single QD-based white QD-based LED (QLED) with a multilayered sequence of PVK hole transport layer (HTL), CGS/ZnS QD emitting layer (EML), and ZnO nanoparticle (NP) electron transport layer (ETL) was fabricated via all-soln. processing. White electroluminescence (EL) that originated only from QDs without any contribution of charge transport layer (CTL) emissions could be obtained of exclusive exciton recombination at EML. Obsd. field-dependent EL spectral variation, showing a steady redn. of low energy EL relative intensity vs. high energy 1 with increasing voltage, was explained jointly with respect to excited-state lifetime and thermal quenching behaviors between DAP vs. CB-to-VCu transitions. Compared to non-Cd QD-based, white EL-capable devices reported so far, the present white QLED that possessed satisfactorily high CRIs of 83-88 exhibited the record EL quantities of 1007 cd m-2 in luminance, 3.6 cd A-1 in current efficiency, 1.91 m W-1 in power efficiency, and 1.9% in EQE. Addnl. fabrication of a white flexible planar QLED and a warm white EL-capable device was fulfilled.
- 20Panda, S. K.; Hickey, S. G.; Demir, H. V.; Eychmüller, A. Bright White-Light Emitting Manganese and Copper Co-Doped ZnSe Quantum Dots Angew. Chem. 2011, 123, 4524– 4528 DOI: 10.1002/ange.201100464
- 21Schreuder, M. A.; Xiao, K.; Ivanov, I. N.; Weiss, S. M.; Rosenthal, S. J. White Light-Emitting Diodes Based on Ultrasmall CdSe Nanocrystal Electroluminescence Nano Lett. 2010, 10, 573– 576 DOI: 10.1021/nl903515g[ACS Full Text], [CAS], Google Scholar21https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXjs1yrtQ%253D%253D&md5=6fe53aab794215002cb68ace8bb525e1White Light-Emitting Diodes Based on Ultrasmall CdSe Nanocrystal ElectroluminescenceSchreuder, Michael A.; Xiao, Kai; Ivanov, Ilia N.; Weiss, Sharon M.; Rosenthal, Sandra J.Nano Letters (2010), 10 (2), 573-576CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)We report white light-emitting diodes fabricated with ultrasmall CdSe nanocrystals, which demonstrate electroluminescence from a size of nanocrystals (<2 nm) previously thought to be unattainable. These LEDs have excellent color characteristics, defined by their pure white CIE color coordinates (0.333, 0.333), correlated color temps. of 5461-6007 K, and color rendering indexes as high as 96.6. The effect of high voltage on the trap states responsible for the white emission is also described.
- 22Bowers, M. M. J.; Ii, M. J. B.; McBride, J. R.; Rosenthal, S. J. White-Light Emission from Magic-Sized Cadmium Selenide Nanocrystals J. Am. Chem. Soc. 2005, 127, 15378– 15379 DOI: 10.1021/ja055470d[ACS Full Text], [CAS], Google Scholar22https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2MXhtFWku7nK&md5=1d3b549fa9a783179bf140812db28957White-Light Emission from Magic-Sized Cadmium Selenide NanocrystalsBowers, Michael J., II; McBride, James R.; Rosenthal, Sandra J.Journal of the American Chemical Society (2005), 127 (44), 15378-15379CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Magic-sized Cd selenide (CdSe) nanocrystals were pyrolytically synthesized. These ultra-small nanocrystals exhibit broadband emission (420-710 nm) that covers most of the visible spectrum while not suffering from self absorption. This behavior is a direct result of the extremely narrow size distribution and unusually large Stokes shift (40-50 nm). The intrinsic properties of these ultra-small nanocrystals make them an ideal material for applications in solid state lighting and also the perfect platform to study the mol.-to-nanocrystal transition.
- 23Nasilowski, M.; Spinicelli, P.; Patriarche, G.; Dubertret, B. Gradient CdSe/CdS Quantum Dots with Room Temperature Biexciton Unity Quantum Yield Nano Lett. 2015, 15, 3953– 3958 DOI: 10.1021/acs.nanolett.5b00838[ACS Full Text], [CAS], Google Scholar23https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXosFGrsr4%253D&md5=eae70bffa7e67747474be7964d57e964Gradient CdSe/CdS Quantum Dots with Room Temperature Biexciton Unity Quantum YieldNasilowski, Michel; Spinicelli, Piernicola; Patriarche, Gilles; Dubertret, BenoitNano Letters (2015), 15 (6), 3953-3958CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)Auger recombination is a major limitation for the fluorescent emission of quantum dots (QDs). It is the main source of QDs fluorescence blinking at the single-particle level. At high-power excitation, when several charge carriers are formed inside a QD, Auger becomes more efficient and severely decreases the quantum yield (QY) of multiexcitons. This limits the efficiency and the use of colloidal QDs in applications where intense light output is required. Here, the authors present a new generation of thick-shell CdSe/CdS QDs with dimensions >40 nm and a compn. gradient between the core and the shell that exhibits 100% QY for the emission of both the monoexciton and the biexciton in air and at room temp. for all the QDs the authors obsd. The fluorescence emission of these QDs is perfectly Poissonian at the single-particle level at different excitation levels and temps., from 30 to 300 K. In these QDs, the emission of high-order (>2) multiexcitons is quite efficient, and the authors observe white light emission at the single-QD level when high excitation power is used. These gradient thick shell QDs confirm the suppression of Auger recombination in gradient core/shell structures and help further establish the colloidal QDs with a gradient shell as a very stable source of light even under high excitation.
- 24Brovelli, S.; Bae, W. K.; Galland, C.; Giovanella, U.; Meinardi, F.; Klimov, V. I. Dual-Color Electroluminescence from Dot-in-Bulk Nanocrystals Nano Lett. 2014, 14, 486– 494 DOI: 10.1021/nl403478s[ACS Full Text], [CAS], Google Scholar24https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhvFejtb7E&md5=9740809fba78d005bc31747890216a00Dual-Color Electroluminescence from Dot-in-Bulk NanocrystalsBrovelli, Sergio; Bae, Wan Ki; Galland, Christophe; Giovanella, Umberto; Meinardi, Francesco; Klimov, Victor I.Nano Letters (2014), 14 (2), 486-494CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)The emission color from colloidal semiconductor nanocrystals (NCs) is usually tuned through control of particle size, while multicolor emission is obtained by mixing NCs of different sizes within an emissive layer. Here, we demonstrate that recently introduced "dot-in-bulk" (DiB) nanocrystals can emit two-color light under both optical excitation and elec. injection. We show that the effective emission color can be controlled by adjusting the relative amplitudes of the core and shell emission bands via the intensity of optical excitation or applied bias in the cases of photoluminescence (PL) and electroluminescence (EL), resp. To investigate the role of nonradiative carrier losses due to trapping at intragap states, we incorporate DiB NCs into functional light-emitting diodes and study their PL as a function of applied bias below the EL excitation threshold. We show that voltage-dependent changes in core and shell emissions are not due to the applied elec. field but rather arise from the transfer of charges between the anode and the NC intragap trap sites. The changes in the occupancy of trap states can be described in terms of the raising (lowering) of the Fermi level for reverse (direct) bias. We find that the applied voltage affects the overall PL intensity primarily via the electron-trapping channel while bias-induced changes in hole-trapping play a less significant role, limited to a weak effect on core emission.
- 25Lee, K.; Han, C.; Kang, H.; Ko, H.; Lee, C.; Lee, J.; Myoung, N.; Yim, S.-Y.; Yang, H. Highly Efficient, Color-Reproducible Full-Color Electroluminescent Devices Based on Red/Green/Blue Quantum Dot-Mixed Multilayer ACS Nano 2015, 9, 10941– 10949 DOI: 10.1021/acsnano.5b05513[ACS Full Text], [CAS], Google Scholar25https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhs1SisL3E&md5=86c660298c2fa977b5e23fd67eedb656Highly Efficient, Color-Reproducible Full-Color Electroluminescent Devices Based on Red/Green/Blue Quantum Dot-Mixed MultilayerLee, Ki-Heon; Han, Chang-Yeol; Kang, Hee-Don; Ko, Heejoo; Lee, Changho; Lee, Jonghyuk; Myoung, NoSoung; Yim, Sang-Youp; Yang, HeesunACS Nano (2015), 9 (11), 10941-10949CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)Over the past few years the performance of colloidal quantum dot-light-emitting diode (QLED) was progressively improved. Most of QLED work was fulfilled as monochromatic device, while full-color-enabling white QLED still remains nearly unexplored. Using red, green, and blue quantum dots (QDs), bichromatic and trichromatic QLEDs were fabricated through sequential soln.-processed deposition of poly(9-vinlycarbazole) (PVK) hole transport layer, 2 or 3 types of QDs-mixed multilayer, and ZnO nanoparticle electron transport layer. The relative electroluminescent (EL) spectral ratios of constituent QDs in the above multicolored devices inevitably vary with applied bias, leading to the common observation of an increasing contribution of a higher-band gap QD EL over low-band gap 1 at a higher voltage. The white EL from a trichromatic device is resolved into its primary colors through combining with color filters, producing an exceptional color gamut of 126% relative to National Television Systems Committee (NTSC) color space that a state-of-the-art full-color org. LED counterpart cannot attain. The trichromatic white QLED also displays the record-high EL performance such as the peak values of 23,352 cd/m2 in luminance, 21.8 cd/A in current efficiency, and 10.9% in external quantum efficiency.
- 26de Nijs, B.; Dussi, S.; Smallenburg, F.; Meeldijk, J. D.; Groenendijk, D. J.; Filion, L.; Imhof, A.; Dijkstra, M.; Van Blaaderen, A. Entropy-Driven Formation of Large Icosahedral Colloidal Clusters by Spherical Confinement Nat. Mater. 2015, 14, 56– 60 DOI: 10.1038/nmat4072[Crossref], [PubMed], [CAS], Google Scholar26https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhsVCrtLfJ&md5=f3d69b41b0a61150dc3b03cc3c9d1945Entropy-driven formation of large icosahedral colloidal clusters by spherical confinementde Nijs, Bart; Dussi, Simone; Smallenburg, Frank; Meeldijk, Johannes D.; Groenendijk, Dirk J.; Filion, Laura; Imhof, Arnout; van Blaaderen, Alfons; Dijkstra, MarjoleinNature Materials (2015), 14 (1), 56-60CODEN: NMAACR; ISSN:1476-1122. (Nature Publishing Group)Icosahedral symmetry, which is not compatible with truly long-range order, can be found in many systems, such as liqs., glasses, at. clusters, quasicrystals, and virus-capsids. To obtain arrangements with a high degree of icosahedral order from tens of particles or more, interparticle attractive interactions are considered to be essential. The authors report that entropy and spherical confinement suffice for the formation of icosahedral clusters consisting of up to 100,000 particles. Specifically, by using real-space measurements on nanometer- and micrometer-sized colloids, as well as computer simulations, the authors show that tens of thousands of hard spheres compressed under spherical confinement spontaneously crystallize into icosahedral clusters that are entropically favored over the bulk face-centered cubic crystal structure. These findings provide insights into the interplay between confinement and crystn. and into how these are connected to the formation of icosahedral structures.
- 27Vanmaekelbergh, D.; van Vugt, L. K.; Bakker, H.; Rabouw, F. T.; de Nijs, B.; van Dijk-Moes, R.; Beasjou, P.; Van Blaaderen, A. Shape-Dependent Multiexciton Emission and Whispering Gallery Modes in Supraparticles of CdSe/Multishell Quantum Dots ACS Nano 2015, 9, 3942– 3950 DOI: 10.1021/nn507310f[ACS Full Text], [CAS], Google Scholar27https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXlvV2gsbs%253D&md5=f4a45ce7db6d89782edccb5869ba568eShape-Dependent Multiexciton Emission and Whispering Gallery Modes in Supraparticles of CdSe/Multishell Quantum DotsVanmaekelbergh, Daniel; van Vugt, Lambert K.; Bakker, Henriette E.; Rabouw, Freddy T.; Nijs, Bart de; van Dijk-Moes, Relinde J. A.; van Huis, Marijn A.; Baesjou, Patrick J.; van Blaaderen, AlfonsACS Nano (2015), 9 (4), 3942-3950CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)Semiconductors are indispensable as the active light-emitting element in many optoelectronic devices. However, even the purest bulk semiconductors suffer from considerable nonradiative recombination leading to low luminescence efficiencies. Zero-dimensional quantum dots show a much better carrier-to-photon conversion caused by confinement of the excitons but suffer from nonradiative recombination when assembled into a solid, due to exciton energy transfer. Here, the authors report on the shape-dependent optical properties of self-assembled supraparticles composed of CdSe/multishell nanocrystals. All supraparticles show stable and bright luminescence in ambient up to high excitation intensities. When the supraparticles are deposited on a Si surface their spherical shape is deformed due to drying. In addn. to single-exciton emission, the authors observe bright emission from multiexciton states at high excitation powers. But supraparticles that retain their perfectly spherical shape show a spectrum with sharp Mie whispering gallery modes, while multiexciton emission is absent.
- 28Mabille, C.; Schmitt, V.; Gorria, P.; Leal Calderon, F.; Faye, V.; Deminière, B.; Bibette, J. Rheological and Shearing Conditions for the Preparation of Monodisperse Emulsions Langmuir 2000, 16, 422– 429 DOI: 10.1021/la990850w[ACS Full Text], [CAS], Google Scholar28https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1MXnsFyjsLs%253D&md5=ddcdd8e275e84b8c3304df1e3d5a1d53Rheological and shearing conditions for the preparation of monodisperse emulsionsMabille, C.; Schmitt, V.; Gorria, Ph.; Calderon, F. Leal; Faye, V.; Deminiere, B.; Bibette, J.Langmuir (2000), 16 (2), 422-429CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)Monodisperse emulsions can be obtained by shearing a crude polydisperse one. The aim was to discover the required conditions for droplet fragmentation and resulting monodispersity, independently of the chem. nature of the system. (i) the role of the initial emulsion viscoelasticity and (ii) the nature of the applied shear were examd. Taking into account these features, a large variety of monodisperse materials is shown that are easily producible in reasonable quantity.
- 29Midgley, P. a.; Weyland, M. 3D Electron Microscopy in the Physical Sciences: The Development of Z-Contrast and EFTEM Tomography Ultramicroscopy 2003, 96, 413– 431 DOI: 10.1016/S0304-3991(03)00105-0[Crossref], [PubMed], [CAS], Google Scholar29https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3sXlsVWqs7w%253D&md5=0189c27492965be8b2e562035c0416a93D electron microscopy in the physical sciences: the development of Z-contrast and EFTEM tomographyMidgley, P. A.; Weyland, M.Ultramicroscopy (2003), 96 (3-4), 413-431CODEN: ULTRD6; ISSN:0304-3991. (Elsevier Science B.V.)A review. The rapid advances in nanotechnol. and the ever decreasing size of features in the microelectronics industry brings with it the need for advanced characterization with high spatial resoln. in two and three dimensions. Stereo microscopy allows some insight into the three-dimensional nature of an object but for true quant. anal., one has to turn to tomog. as a way to reconstruct a three-dimensional object from two-dimensional projections (images). X-ray tomog. allow structures to be imaged at relatively large length scales, atom probe tomog. at the at. level. Electron tomog. offers an intermediate resoln. (of ∼1 nm) with a field of view of hundreds of nm making it ideal for the characterization of many nanoscale devices. While electron tomog. was used in the biol. sciences for >30 yr, it is only now being applied to the phys. sciences. The authors review the status of electron tomog., describe the basis behind the technique and some of the practicalities of recording and analyzing data for tomog. reconstruction, particularly in regard to solving three-dimensional problems that are encountered in materials science at the nanometer level. The authors present examples of how STEM dark-field imaging and energy-filtered TEM can be used successfully to examine nearly all types of specimens likely to be encountered by the phys. scientist.
- 30Altantzis, T.; Goris, B.; Sánchez-Iglesias, A.; Grzelczak, M.; Liz-Marzán, L. M.; Bals, S. Quantitative Structure Determination of Large Three-Dimensional Nanoparticle Assemblies Part. Part. Syst. Charact. 2013, 30, 84– 88 DOI: 10.1002/ppsc.201200045[Crossref], [CAS], Google Scholar30https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38Xhs1OgsLzO&md5=fd3d02dfb17346524ddbdc18e672b810Quantitative Structure Determination of Large Three-Dimensional Nanoparticle AssembliesAltantzis, Thomas; Goris, Bart; Sanchez-Iglesias, Ana; Grzelczak, Marek; Liz-Marzan, Luis M.; Bals, SaraParticle & Particle Systems Characterization (2013), 30 (1), 84-88CODEN: PPCHEZ; ISSN:1521-4117. (Wiley-VCH Verlag GmbH & Co. KGaA)This study proposed an improved route towards the quant. structure detn. of large 3D nanoparticle assemblies, which required optimization of both the acquisition technique and the reconstruction algorithm. Generally, data revealed that 3D quant. results for large nanoparticle assemblies can be obtained by optimizing different aspects of the electron tomog. expt. For the acquisition, HAADF-STEM imaging is less suited and IBF-STEM imaging, cor. for the so-called cupping artifact presents the best alternative. The total variation minimization technique is presented as the most optimal approach for the 3D reconstruction. In fact through this methodol., a large (>500 nm) spherical assembly of Au nanoparticles was reconstructed while minimizing any artifacts in the reconstruction.
- 31Steinhardt, P. J.; Nelson, D. R.; Ronchetti, M. Bond-Orientational Order in Liquids and Glasses Phys. Rev. B: Condens. Matter Mater. Phys. 1983, 28, 784– 805 DOI: 10.1103/PhysRevB.28.784[Crossref], [CAS], Google Scholar31https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL3sXkslOgs7w%253D&md5=28361a8f41e7dd34826a01d7ae4e5e08Bond-orientational order in liquids and glassesSteinhardt, Paul J.; Nelson, David R.; Ronchetti, MarcoPhysical Review B: Condensed Matter and Materials Physics (1983), 28 (2), 784-805CODEN: PRBMDO; ISSN:0163-1829.Bond orientational order in mol. dynamics simulations of supercooled liqs. and in models of metallic glasses is studied. Quadratic and 3rd-order invariants formed from bond spherical harmonics allow quant. measures of cluster symmetries in these systems. A state with short-range translational order, but extended correlations in the orientations of particle clusters, starts to develop about 10% below the equil. melting temp. in a supercooled Lennard-Jones liq. The order is predominantly icosahedral, although there is also a cubic component which we attribute to the periodic boundary conditions. Results are obtained for liqs. cooled in an icosahedral pair potential as well. Only a modest amt. of orientational order appears in a relaxed Finney dense-random-packing model. In contrast, essentially perfect icosahedral bond correlations are found in alternative "amorphon" cluster models of glass structure.
- 32Wang, Y.; Teitel, S.; Dellago, C. Melting of Icosahedral Gold Nanoclusters from Molecular Dynamics Simulations J. Chem. Phys. 2005, 122, 214722 DOI: 10.1063/1.1917756[Crossref], [PubMed], [CAS], Google Scholar32https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2MXlsVeku7s%253D&md5=3948915e1b48f6c0fc0f764b1f2d3823Melting of icosahedral gold nanoclusters from molecular dynamics simulationsWang, Yanting; Teitel, S.; Dellago, ChristophJournal of Chemical Physics (2005), 122 (21), 214722/1-214722/16CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)Mol. dynamics simulations show that Au clusters with about 600-3000 atoms crystallize into a Mackay icosahedron upon cooling from the liq. A detailed surface anal. shows that the facets on the surface of the Mackay icosahedral gold clusters soften but do not premelt below the bulk melting temp. This softening is found to be due to the increasing mobility of vertex and edge atoms with temp., which leads to inter-layer and intra-layer diffusion, and a shrinkage of the av. facet size, so that the av. shape of the cluster is nearly spherical at melting.
- 33van Driel, A. F.; Allan, G.; Delerue, C.; Lodahl, P.; Vos, W. L.; Vanmaekelbergh, D. Frequency-Dependent Spontaneous Emission Rate from CdSe and CdTe Nanocrystals: Influence of Dark States Phys. Rev. Lett. 2005, 95, 236804 DOI: 10.1103/PhysRevLett.95.236804[Crossref], [PubMed], [CAS], Google Scholar33https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2MXht1Oru7nF&md5=7d8ddd3865cfbf83241a469db532e440Frequency-Dependent Spontaneous Emission Rate from CdSe and CdTe Nanocrystals: Influence of Dark Statesvan Driel, A. F.; Allan, G.; Delerue, C.; Lodahl, P.; Vos, W. L.; Vanmaekelbergh, D.Physical Review Letters (2005), 95 (23), 236804/1-236804/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)The authors studied the rate of spontaneous emission from colloidal CdSe and CdTe nanocrystals at room temp. The decay rate, obtained from luminescence decay curves, increases with the emission frequency in a supralinear way. This dependence is explained by the thermal occupation of dark exciton states at room temp., giving rise to a strong attenuation of the rate of emission. The supralinear dependence is in agreement with the results of tight-binding calcns.
- 34Verhaegh, N. A. M.; van Blaaderen, A. Dispersions of Rhodamine-Labeled Silica Spheres: Synthesis, Characterization, and Fluorescence Confocal Scanning Laser Microscopy Langmuir 1994, 10, 1427– 1438 DOI: 10.1021/la00017a019[ACS Full Text], [CAS], Google Scholar34https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2cXivVWiu7c%253D&md5=dce78e9d12343d9404e3921c65f4e280Dispersions of Rhodamine-Labeled Silica Spheres: Synthesis, Characterization, and Fluorescence Confocal Scanning Laser MicroscopyVerhaegh, Nynke A. M.; Blaaderen, Alfons vanLangmuir (1994), 10 (5), 1427-38CODEN: LANGD5; ISSN:0743-7463.Monodisperse colloidal silica spheres were synthesized with a total radius of 200 nm and labeled with the fluorescent dye rhodamine isothiocyanate (RITC) in a core of 100 nm radius. The particles were characterized by TEM and by static and dynamic light scattering. The fluorescence properties and dye concns. in the particles were measured with fluorescence and absorption spectroscopy. Stable dispersions of these hydrophilic, charge-stabilized silica spheres in polar solvents and of organophilic, sterically stabilized, 1-octadecanol-coated silica spheres in apolar solvents were studied with fluorescence confocal scanning laser microscopy (CSLM). The bleachability of these particles was detd. with CSLM and compared with particles labeled with the dye fluorescein isothiocyanate (FITC). The possibilities and limitations of confocal microscopy to study individual fluorescent particles in the bulk of concd. model dispersions are discussed and demonstrated with CSLM graphs of a time series showing colloidal crystn. (crystal growth rate ∼ 4 μm/s), an equil. between a colloidal liq. and colloidal crystal interface, and a binary mixt. of RITC- and FITC-labeled spheres. Further, the feasibility of by using the RITC-labeled spheres with other techniques relying on fluorescence is also discussed.
- 35Li, J. J.; Wang, Y. A.; Guo, W.; Keay, J. C.; Mishima, T. D.; Johnson, M. B.; Peng, X. Large-Scale Synthesis of Nearly Monodisperse CdSe/CdS Core/Shell Nanocrystals Using Air-Stable Reagents via Successive Ion Layer Adsorption and Reaction J. Am. Chem. Soc. 2003, 125, 12567– 12575 DOI: 10.1021/ja0363563[ACS Full Text], [CAS], Google Scholar35https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3sXnsVOisLs%253D&md5=8d5e57d2c474afe888f40b37069364deLarge-Scale Synthesis of Nearly Monodisperse CdSe/CdS Core/Shell Nanocrystals Using Air-Stable Reagents via Successive Ion Layer Adsorption and ReactionLi, J. Jack; Wang, Y. Andrew; Guo, Wenzhuo; Keay, Joel C.; Mishima, Tetsuya D.; Johnson, Matthew B.; Peng, XiaogangJournal of the American Chemical Society (2003), 125 (41), 12567-12575CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Successive ion layer adsorption and reaction (SILAR) originally developed for the deposition of thin films on solid substrates from soln. baths is introduced as a technique for the growth of high-quality core/shell nanocrystals of compd. semiconductors. The growth of the shell was designed to grow 1 monolayer at a time by alternating injections of air-stable and inexpensive cationic and anionic precursors into the reaction mixt. with core nanocrystals. The principles of SILAR were demonstrated by the CdSe/CdS core/shell model system using its shell-thickness-dependent optical spectra as the probes with CdO and elemental S as the precursors. For this reaction system, a relatively high temp., ∼220-240°, is essential for SILAR to fully occur. The synthesis can be readily performed on a multigram scale. The size distribution of the core/shell nanocrystals was maintained even after 5 monolayers of CdS shell (equiv. to ∼10 times vol. increase for a 3.5 nm CdSe nanocrystal) were grown onto the core nanocrystals. The epitaxial growth of the core/shell structures was verified by optical spectroscopy, TEM, XRD, and XPS. The luminescence quantum yield (PL QY) of the as-prepd. CdSe/CdS core/shell nanocrystals ranged from 20% to 40%, and the PL full-width at half-max. (fwhm) was maintained between 23 and 26 nm, even for those nanocrystals for which the UV-visible and PL peaks red shifted by ∼50 nm from that of the core nanocrystals. Several types of brightening phenomena were obsd., some of which can further boost the PL QY of the core/shell nanocrystals. The CdSe/CdS core/shell nanocrystals are superior in comparison to the highly luminescent CdSe plain core nanocrystals. The SILAR technique reported here can also be used for the growth of complex colloidal semiconductor nanostructures, such as quantum shells and colloidal quantum wells.
- 36Bae, W. K.; Kwak, J.; Park, J. W.; Char, K.; Lee, C.; Lee, S. Highly Efficient Green-Light-Emitting Diodes Based on [email protected] Quantum Dots with a Chemical-Composition Gradient Adv. Mater. 2009, 21, 1690– 1694 DOI: 10.1002/adma.200801908[Crossref], [CAS], Google Scholar36https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXltFGhsr0%253D&md5=8b102d3383d4cab287124d60c8bc0e61Highly Efficient Green-Light-Emitting Diodes Based on [email protected] Quantum Dots with a Chemical-Composition GradientBae, Wan Ki; Kwak, Jeonghun; Park, Ji Won; Char, Kookheon; Lee, Changhee; Lee, SeonghoonAdvanced Materials (Weinheim, Germany) (2009), 21 (17), 1690-1694CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)The Green-emitting LEDs based of quantum dots were fabricated and their properties studied. The spectral properties of prepd. films were obtained and EL and current efficiency for diodes were discussed.
- 37Lee, K.; Lee, J.; Song, W.; Ko, H.; Lee, C.; Lee, J.; Yang, H. Higly Efficient, Color-Pure, Color-Stable Blue Quantum Dot Light-Emitting Devices ACS Nano 2013, 7, 7295– 7302 DOI: 10.1021/nn402870e
- 38van Aarle, W.; Palenstijn, W. J.; De Beenhouwer, J.; Altantzis, T.; Bals, S.; Batenburg, K. J.; Sijbers, J. The ASTRA Toolbox: A Platform for Advanced Algorithm Development in Electron Tomography Ultramicroscopy 2015, 157, 35– 47 DOI: 10.1016/j.ultramic.2015.05.002[Crossref], [PubMed], [CAS], Google Scholar38https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXotVKhsLs%253D&md5=3712da2f93e931cb64ef3c7e65dee01eThe ASTRA Toolbox: A platform for advanced algorithm development in electron tomographyvan Aarle, Wim; Palenstijn, Willem Jan; De Beenhouwer, Jan; Altantzis, Thomas; Bals, Sara; Batenburg, K. Joost; Sijbers, JanUltramicroscopy (2015), 157 (), 35-47CODEN: ULTRD6; ISSN:0304-3991. (Elsevier B.V.)We present the ASTRA Toolbox as an open platform for 3D image reconstruction in tomog. Most of the software tools that are currently used in electron tomog. offer limited flexibility with respect to the geometrical parameters of the acquisition model and the algorithms used for reconstruction. The ASTRA Toolbox provides an extensive set of fast and flexible building blocks that can be used to develop advanced reconstruction algorithms, effectively removing these limitations. We demonstrate this flexibility, the resulting reconstruction quality, and the computational efficiency of this toolbox by a series of expts., based on exptl. dual-axis tilt series.
- 39van Aarle, W.; Palenstijn, W. J.; Cant, J.; Janssens, E.; Bleichrodt, F.; Dabravolski, A.; Beenhouwer, J. De; Batenburg, K. J.; Sijbers, J. Fast and Flexible X-Ray Tomography Using the ASTRA Toolbox Opt. Express 2016, 24, 25129– 25147 DOI: 10.1364/OE.24.025129[Crossref], [PubMed], [CAS], Google Scholar39https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC2snksFaqtA%253D%253D&md5=5bebcfefa69d3bc59e8184d9adf1e0ffFast and flexible X-ray tomography using the ASTRA toolboxvan Aarle Wim; Palenstijn Willem Jan; Cant Jeroen; Janssens Eline; Bleichrodt Folkert; Dabravolski Andrei; De Beenhouwer Jan; Joost Batenburg K; Sijbers JanOptics express (2016), 24 (22), 25129-25147 ISSN:.Object reconstruction from a series of projection images, such as in computed tomography (CT), is a popular tool in many different application fields. Existing commercial software typically provides sufficiently accurate and convenient-to-use reconstruction tools to the end-user. However, in applications where a non-standard acquisition protocol is used, or where advanced reconstruction methods are required, the standard software tools often are incapable of computing accurate reconstruction images. This article introduces the ASTRA Toolbox. Aimed at researchers across multiple tomographic application fields, the ASTRA Toolbox provides a highly efficient and highly flexible open source set of tools for tomographic projection and reconstruction. The main features of the ASTRA Toolbox are discussed and several use cases are presented.
- 40Palenstijn, W. J.; Batenburg, K. J.; Sijbers, J. Performance Improvements for Iterative Electron Tomography Reconstruction Using Graphics Processing Units (GPUs) J. Struct. Biol. 2011, 176, 250– 253 DOI: 10.1016/j.jsb.2011.07.017[Crossref], [PubMed], [CAS], Google Scholar40https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC3Mfnslygsw%253D%253D&md5=7799f40ff4990fbf11f37f13d421aa74Performance improvements for iterative electron tomography reconstruction using graphics processing units (GPUs)Palenstijn W J; Batenburg K J; Sijbers JJournal of structural biology (2011), 176 (2), 250-3 ISSN:.Iterative reconstruction algorithms are becoming increasingly important in electron tomography of biological samples. These algorithms, however, impose major computational demands. Parallelization must be employed to maintain acceptable running times. Graphics Processing Units (GPUs) have been demonstrated to be highly cost-effective for carrying out these computations with a high degree of parallelism. In a recent paper by Xu et al. (2010), a GPU implementation strategy was presented that obtains a speedup of an order of magnitude over a previously proposed GPU-based electron tomography implementation. In this technical note, we demonstrate that by making alternative design decisions in the GPU implementation, an additional speedup can be obtained, again of an order of magnitude. By carefully considering memory access locality when dividing the workload among blocks of threads, the GPU's cache is used more efficiently, making more effective use of the available memory bandwidth.
- 41Schlossmacher, P.; Klenov, D. O.; Freitag, B.; von Harrach, H. S. Enhanced Detection Sensitivity with a New Windowless XEDS System for AEM Based on Silicon Drift Detector Technology Microsc. Today 2010, 18, 14– 20 DOI: 10.1017/S1551929510000404[Crossref], [CAS], Google Scholar41https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXhtVajsrfF&md5=e80c6540f5bbcd30846eb8d3cbd1389aEnhanced detection sensitivity with a new windowless XEDS system for AEM based on silicon drift detector technologySchlossmacher, P.; Klenov, D. O.; Freitag, B.; von Harrach, H. S.Microscopy Today (2010), 18 (4), 14, 16, 18-20CODEN: MITOFQ; ISSN:1551-9295. (Cambridge University Press)A new X-ray energy dispersive spectrometer (XEDS) system is described and application examples from a new anal. electron microscope (AEM) system are presented. The novel ChemiSTEM technol. on the Tecnai Osiris comprises this new proprietary XEDS detector system (Super-X design) in combination with a high- brightness Schottky field emission electron source (X-FEG) as the two major components. In addn. to the Schottky FEG source, the new detector system shows greatly enhanced detection sensitivity due to four detectors integrated deeply into the objective lens, windowless silicon drift detector technol. with shutters, and high-speed electronics readout. This new system architecture provides many performance benefits, such as improved light element detection, better sample tilt response, faster mapping, and esp. enhanced system detection sensitivity.
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ARTICLE SECTIONSThe Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsnano.7b03975.
Synthesis of core/multishell QDs, optical characterization of the QDs, synthesis of the SPs, determination of the quantum yield of QDs and SPs, determination of the RDF and CIE coordinates (PDF)
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